TID-4500, UC-25 Metals, Ceramics, and Materials
[3 LAWRENCE UVBRMORE LABORATORY
UCRL-51269 FINAL REPORT OF THE LIGHT ARMOR MATERIALS PROGRAM R. L. Landingham A. W. Casey
MS. date: September 15, 1972
-NOTICE- Thli report wu prepared as in account of work sponsored by the United States Government, Neither Ihe United Stit«s nor the United Stales Atomic Energy Commission, not any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or Implied, or assumes any legal liability or responsibility for the accuracy, com pleteness or usefulness of any Information, apparatus, product or process disclosed, of represents that Its use would not infringe privately owned rights.
me —•"—tmrnimmtiun Foreword
This report covers the work performed on the August 1970 extension of the Advanced Research Projects Agency (ARPA) order 980. This effort was directed to ward the development of light armor materials. The 'nltial concepts behind the development of these materials are described in previous LLL reports. 1-5 Contents
Foreword jfi Abstract 1 Introduction 2 The Effect of Composition and Microstructure on Ballistic Performance
of Be2B and Be4B 4 Hot-Pressed Targets 4 Hot-Pressing 4 Reaction Hot-Pressing 5 Grain Size g Fracture Mechanism 11 Process Variables 17 Cast Targets 22 Directional Solidification 23 Grain Nucleation ...... 24 The Ballistic Performance of Metal-Graded or Reinforced Beryllium Boride Armor 25
Be4B-Be 26 Be.B-Nl or Ni Based AUoy 29 Toxicity Studies 30 Environmental Tests 36 Summary 40 Acknowledgments 41 Appendix A. Preparation of Materials and Analytical Evaluation ... 42 Appendix B. Average Griin Size Determination 45 Appendix C. Evaluation of Fractured Surfaces with Electron Microscopic Techniques 46 Appendix D. The Collection and Characterization of Powders Generated by Ballistic Impact 47 References 49
-v- FINAL REPORT OF THE LIGHT ARMOR MATERIALS PROGRAM
Abstract
Beryllium boride compounds have been discussed. It has been shown that grain evaluated as potential materials for use in size can in some cases be controlled by light armor applications. Target speci process variables. Toxicity Investigations mens have been prepared by hot-pressing Have also been carried out. As a part of and casting techniques and subjected to these toxicity studies the amount and size ballistic testing. In each case, ballistic distribution of ballistic debris has been performance was found to be strongly determined. Environmental studies have related to composition and to the micro- shown the beryllium borides to be resistant structure of the target material. One to high temperature oxidation and thermal important microstructural feature has shock, but adversely affected by salt been found to be the grain size of the water. A working Be-B phase diagram is target material. The mechanism of also provided. The ballistic performance fracture is described and the relationship of beryllium borides was improved when they of the type of fracture to grain size were incorporated in m etal- graded targets.
Introduction
Studies conducted at these laborato- Several ceramics (i.e. B4C, AlgOg, SiC, ries 1-5 have led to a better understanding AIB12I possess the qualities of low density of penetration mechanics. Knowledge of and high incompressibility, but even at high the important material parameters that hydrostatic confining pressures, only a few operate during the penetration process low-density ceramics (BeO, BegB, Be4B, has uelped reveal the path to be taken in and MgO) show ductility. However, ductility the development of materials for use as can be incorporated in some ceramics by light armor. In general, the ideal mate addition of the proper metal to form a cermet. rial should exhibit the proper blanace An improvement in ballistic performance by between low density, high incompress- the addition of metal, and the existenceof an ibility (high yield strength and impedance) optimum in metal concentration have been and the ability to dissipate tensile previously demonstrated with the TiC-Ni- stresses without fracturing (ductility). Mo system. Unfortunately, no cermets A detailed evaluation of these material having both low density (<3.0 g/cc) and parameters has been previously high incompressibility have been hereto described.^.* fore developed.
-1- Beryllium borldes have the above prop actually reduces the density of the ceramic. erties plus the capability of forming low Increasing the beryllium metal content density cermets. Indeed, combining leads to a more ductile cermet. The beryllium metal with beryllium borlde ductile behavior of beryllium has been
Table 1. Ballistic limits for various ceramics bonded to 0.25-in. 6061-T6 aluminum.
Density b d a V c A BL A2700 p°A2700 Ceramic (g/cc) (in.) (ft/sec) (in.) (g/cm2) *S
B4C 2.50 0.290 2700 ± 50 0.29 1.84 1.00 BeO 2.84 0.250 2500 ± 50 0.27 1.95 0.94 BeO + B 2.50 0.250 2320 ± 80 0.29 1.84 1.00 Coors AD85 2.79 alumina 3.43 0.340 2850 ± 50 0.32 0.66 Coors AD999 alumina 3.96 0.250 2660 ± 80 0.25 2.51 0.73 WESG" 995 2.79 alumina 3.85 0.303 2870 ± 50 0.285 0.66 Diamonite alumina 3.72 0.340 3170 ± 50 0.29 2.74 0.67 Carborundum hot-pressed 3.92 0.250 2550 ± 50 0.26 2.59 0.71 alumina Sapphire 3.98 0.250 2470 ± 80 0.27 2.73 0.67 Si 2.33 0.250 1200 ± 50 0.56 3.31 0.56 SIC 3.09 0.250 2175 ±75 0.31 2.43 0.76
Si3N4 2.815 0.355 1450 ± 50 0.(56 4.72 0.39 Quartz Ite 2.58 0.250 1250 ±100 0.54 3.54 0.52 B 2.36 0.22tf 2100 ±80 0.29 1.74 1.06
A1B12 2.53 0.250 2250 ± 80 0.30 1.93 0.95
Be2B 2.03 0.250 2150 ± 50 0.31 1.60 1.15
T1B2 4.46 0.236 2270 ± 50 0.28 3.17 0.56
TiBe12 2.25 0.250 2250 ±100 0.30 1.74 1.06 Pure 0.27 TIC 4.88 0.25 2500 ± 80 3.25 0.55 TiC + (Ni.Mo) cermet 5.63 0.25 3050 ± 80 0.22 3.15 0.58 WC-(k-a) 15.24 0.25 3300 ± 200 0.20 7.7 0.24 A = ceramic thickness. VBL experimental ballistic limit. A2700 = extrapolated ceiimic thickness for V = 2700 ft/sec BmL > ceramic areal density.
$ - B4C areal density/ceramic areal density.
-2- demonstrated under hydrostatic confining Be-B armor for specific applications were pressures of 6 to 63 kb*r at relatively low considered unrealistic during early stages strain rates (3 X 10 sec ). In view of of the program. Evaluation studies were the above facts, we undertook to explore directed instead toward more general the possibility of using beryllium boride areas in the expectation that such results systems in light armor applications. would be useful in selecting ar.d designing Extensive evaluation of the promising specific applications in the future. The Be-B compounds (Be.B and Be.B) was general areas studied were the relation initiated after exceptionally high ballistic ship of composition and mlcrostructure performances4* had been obtained on to ballistic performance, the effect of many preliminary test specimens. Bal fabrication processes on mlcrostructure, listic performances of several materials the ballistic performance of metal-graded are compared in Table 1 and Figs. 1 and 2. or reinforced beryllium borlde armor, A detailed description of the Be-B system beryllium boride toxicity, and environmental is given in Appendix A. Efforts to prepare effects on beryllium borides.
4000 1 1 1 1 -1— 1 1 1 T 1 1 1 1 1 1 1 1
Ceramic—. jS~ 6061-T6 aluminum 3500 - >l LRt. .30-cal sharp S BeO projectile—•»
S 3000 - — 0.25 in. _S^ > S
> 2500
Tifie12— limit . u ' ^,"-"DAD-85 alumina 2000 1 (alii :
"^ V ± 50 ft/sec s *<»' BL 1000 1 1 1 1 _L_ J 1_ _•_ i. _i .1 i I.I • 1 i 1.0 1.5 2.0 2.5 Ceramic areal density, p" A — g/cm
c Fig. 1. Ballistic limit versus ceramic areal density for aluminum backed ceramic targets." -3- 1.4
Ceromic facing "^ Fiborgloss .30-cal (REPCO 1.3 APM2 woven projectile- roving) 8a48 with
SI 1.2 h-6
+ 1.1 Be ,B graded u 'i with Bo metal
B4C l.o
g 0.9-
0.8
VBL±50ft/sec
0.7 -L 1500 2000 2500 3000 Ballistic limit, Vg, — ft/sec
Fig, 2. Ballistic limit of targets with various ceramic impact surfaces compared to targets with B4C impact surfaces.5
The Effect of Composition and Microstructure on Ballistic Performance of Be2B and Be4B
HOT-PRESSED TARGETS temperatures ( -4- • The die was next heated to the desired peratures were required to achieve dense temperature under minimum pres f>98% of theoretical) disks if the BeO or sure (<500 psl). higher boride contaminates (Be2B, BeB2, • The desired pressure was applied at etc) exceeded -3 wt% in Be.B or Be2B. temperature and the powder allowed to consolidate. Reaction Hot-Pressing • The pressure was released and the Reaction hot-pressing of stoichiometric disk removed from the die at £400°C. blends of Be and B powder Is an alternative Since no ballistic degradation was found to approach to the fabrication of Be.B and occur when the targets were extracted hot Be„B targets by hot-pressing. This (£800°C) from the dies and cooled, degrada approach offers a substantial saving in tion by thermal shocking was not considered cost since It eliminates synthesis of the to be a problem under the above conditions. starting materials. Heating of the hot-press dies was accom The Be and B powders were blended plished by one of the following methods: together in batches of £ ktf or less by induction heating of the graphite die in an either wet or dry ball milling in 2 quart argon atmosphere, resistance heating of A1„03 or WC ball mills. A uniform blend elements around the graphite die in an of fine powders is essential In obtaining argon atmosphere, or resistance heating a uniform, predominantly one phase (>90%) of the graphite die in an air atmosphere. microstructure. The general hot-pressing Typical experimental conditions for the procedure just described was also used for reaction hot-pressing, with the excep fabrication of Be4B and Be2B targets are listed in Table 2. Slightly higher tem tion that the blended powders were held at Table 2. Summary table of hot-preesing and1 reaction hot-pressing parameters for Be4B and Be,B. Consolidation Heating Cooling Desired Powder Typo of time Temp Pressuro Tijno time Typical density composition charged heotlnga Atmosphere (min) IX) ipsl) (mln) (mln) g/ec b d Be2B Be2B l Argon 20 1105 EtlDO 10 ISO 2.06 100 30 b 4000 2.03 d Be2B Be2B a Argon 1060 4 180 I07 C Be2B BD2B 3 Air 20 10D5 4000 5 GO 2.08 xufi Be2B Bo + B 3 Air 20 1065° 4000 B 00 2.10 111" b Be4B Ba4B 2 Argon 20 toio 5000 7 ISO 1.02 08.7 b Be„B Bo4B 2 Argon 30 1075 4000 7 ISO 1.32 88.7° c Be4B B=4B 3 Air 20 1040 4000 5 60 1.94 09.7 Be4B BetB 3 Air 20 1030° 4000 8 60 1.04 09.7" C 4 volfo BeO- BeO * Be4B 3 Air 20 1075 4000 S GO i.oa 100.5° Bc4B 4 vol?- Al.O,- Al-O,- 3 • Air 20 I055c 4000 5 60 2.03 100.0 2 3 3 Be4B Be^B 1 — Induction heating of graphite die. 2—Resistance heating of elements around graphite die. 3—Resistance heating of graphite die. Optical pyrometer readings (4l5°C>. cPt-Rh thermocouple readings {±7°C(. Contaminated with BeB2 and BeO. Contaminated with 3 to 5 */l% BeO. -5- temperature for 3 to 5 min before the final Be) were found to be present in early 3-5 pressure of 3000 to 4500 psi was applied. targets. When these minor phases Disks were generally hot-pressed in the were reduced (<2 volfl) in Bo.B targets, resistance heated graphite dies since this a corresponding reduction (33%) in bal procedure was fastest. Typical reaction listic performance was noted. However, hot-pressing parameters are given in ?0% o.' this reduction could be restored by Table 2. dispersing a minor phase (10 volTo, The fine particle size of amorphous <44 JJdiam, Be2B) in the high purity Be.B boron powder (<1 ,u diam) is well suited to powder prior to the hot-pressing operation. this process. On the other hand, incom The early ballistic performance of Be.B plete reaction of larger Be particles was completely restored by the similar (>20 fi diam) was revealed by microhardness dispersal of 4 vol% of BeO powder (<2 n tests and metallography (Fig. 3). The diam) in the high purity Be.B powder. microhardness of the Be (gray phase) Since these results indicate a dependence grains was <600 If?/mm2 and the Be.B of ballistic performance on composition; 2 matrix was > 1300 kg/mm . Beryllium the effect of composition on microstruc powder lota with smaller particle sizes ture, and microstructure on ballistic per have since been used to improve the uni formance was further investigated. formity of the microstructure. Some Several mechanisms can be postulated typical beryllium particle-size distribu to explain the role of impurities in tions are shown in Fig. 4. improving the ballistic performance of Be.B. One possible explanation involves Grain Size dispersion-strengthening of the matrix Various combinations of well dispersed material. If dispersion-strengthening of minor phases (BeO. Be«B, Be.B and/or Be.B with BeO were operative, increased microhardness and improved ballistic per formance should be expected with finer- grained dispersions of BeO. Such finer dispersions were prepared by oxidizing the surface of the Be.B powder before Particle diameter — n Fig. 3. Reaction hot-pressed Be4B. Note the large unreacted particles of Fig. 4. Particle-size distribution of Be (gray phase). beryllium powder. -6- hot-pressing. The resulting targets resulted In a 50?o rise in VB, (Fig. 5). (5.8 vol% BeO-Be4B) had the same ballistic The existence of an optimum size wus performance and microhardness as the first suggested by the observation that a 4 vol% BeO-Be4B powder blended targets. further increase in grain density to The high-purity Be.B had the same micro- 0.12 gratns/u2 had littte effect on V„, hardness as both of the compositions con DU (Fig. 5). This concept was verified by taining BeO. Thus, dispersion-strengthening observing the effect of a further increase evidently does not explain the role of BeO in grain density (Fig. 6). Additional con in improving the ballistic performance of firmation that grain size exerts a strong Be.B targets. influence on ballistic performance comes Another mechanism Involves the role from further inspection of Fig. 6. It can of impurities In interfering with crack be seen that targets 2 and 3, which had the propagation. This effect will be dis highest ballistic limits, also had lower BeC cussed In the section on Fracture Mech contents (St .8 vol%) than targets 1 and 5 anism. (53.5 vol% BeO). The influence of grain Alteration of the target grain size by size was greater than that of composition. impurities is another possibility. The The effect of BeO particles on the bal n Heyn's intercept method was used to listic performance of Be.B was comparer, with that of A1 0 particles. A slight determine the average number of grains ? 3 decrease in V , was observed when 4 VJ1% per unit area, or average grain density. Q ot AlnO, powder (ultraflne polishing c< ;i- It is important to keep in mind that an pountt) was blendod with high-purity i:- B Increase in the average number of grains 4 powder. Note the similarity in grain den or grain density represents a decrease in sities of targets 1 and 4 in Fig. 6. X-ray grain size. Even though the actual sizes diffraction studies of these hot-pressed of the grains are larger than the calcula powder blends indicated that neither Al 0~ tion indicates (see Appendix B), these 2 nor BeO were soluble in Be.B. These relative values are useful for purposes of minor phases appeared mainly as fine comparison. particles in the grain boundaries A marked correlation between grain (Fig. 7). size and ballistic limit (V ,) was found" B Grain size has also been observed to (Figs. 5 and 6). An increase in the aver affect the ballistic performance of Be„B age number of grains per unit area (aver- n targets. Targets ware hot-pressed from age grain density) from 0.022 grains/ji to Be„B powder after tile powder lot had 0.052 grains/^ (decrease in grain size) been separated into two size-fractions In tests using fiberglass reinforced (20 fi to 37 v and 5 to 20 n). The grain plastic backup plates and .30 cal U. S. Army AP projectiles, a high degree of density of the target hot-pressed from the data scatter was noted (Fig. 5). We found powder of larger particle size was that by using sharp point projectiles made 0.1 grains/fi and its ballistic velocity of Allegheny 609 steel and Be4B targets backed with 6061-T6 aluminum we were 2500 it/sec, while the values for the able to reduce data scatter and detect the effects of smaller changes in target smaller sized fraction were 0.13 grains/ materials (Fig. 6). /j2 and 2400 ft/sec. -7 1900 V Reaction hot pressed a 6 vol% BeO 1800 4 vol% BeO 1700 8 * 1600 I )10 vo'%8e2B e ^ 1500 1 i'm 1300 1200 - ?' 2 vol% impurities - Predominantly | I Predominantly fransgranular ••• Transition region —*•"{ intergranular fracture !, j fracture 1100 i • i! • i 0.04 0.08 0.12 0.16 0.20 Average grain density — grains/u. Fig. 5. Ballistic limits of Be4B with various impurity levels versus average grain density. The thicknesses of the Be^B and aluminum backup plates were constant. -8- 2800 2700 /-\ T/ 260O I 2500 / / / / .-s 2400 E tfr £ 2300 PredominantlQy I Predominantly fransgranular • Transition region • -lintergranular fracture {fracture 2200 (j_) Hot-pressed Be.B powder (<44 u. diam) 3.5 vol %BeO (J) Hot-pressed Be. B powder (<20 H dlom) 1.8 vol %BeO (3) Hot-pressed Be. B powder (< 44 H diom), fl-2 vol %AI203 2100 - balf-milled in AI,Oo mill 11.8 vol %BeO \AJ Hot-pressed powder blend of AljOg-Be.B 4 vol %AI203 [5j Reaction hot-pressed Be. B 6 vol %8eO 2C00 0.04 0.08 0.12 0.16 0.20 Average grain density — grains/V Pig. 6. Ballistic limit versus average grain density for Be.B targets with fiberglass backup plates. o. 4 vol%BaO-Be4B b. 4 vol% AI203-8e4B Fig. 7. Typical microstructures of hot-preaaed B124B prepared from blends of Be4B powder (2-44 n diam) and either 4 vol% of BeO (a) or Al,Oq powder (<2 » diam) (b). * J The BeO content in these two powder or sintered ceramics have also been fractions and the resultant hot-pressed observed. A significant increase (12.2%) targets was relatively low (<3%) according to x-ray diffraction. Traces of Be.B were detected in the powders but not in the hot-pressed targets. The presence of BeB, in the hot-pressed Be,B was varified from microhardness tests and metallog raphy. The lighter phase (BeB,) in Fig. 8 had a Knoop microhardness of >2000 kg/ mm (100 g load), while the hardness of the 9 matrix phase (Be„B) was -1300 kg/mm (100 g load). Identification of amounts less than 40 vol% of BeB, in BeO con taminated BeoB is difficult since the two compounds have overlapping x-ray diffrac tion patterns. More extensive efforts will Fig. 8. Typical microstructure of target be made to identify this minor phase in the hot-pressed from fine (<20^i) Be2B powder. The microcracka course of determining the entire Be-B were induced during ballistic phase diagram. testing. The target was etched for 15 sec in HN03:HF:H20 Similar effects of grain size on the (10:2:88 by vol) to improve res ballistic performance of other hot-pressed olution. 10- in ballistic limit was obtained with an postulated, that where BeO is concentrated, AlgO„ target of fine grain size. The bal the fracture does not traverse the boundary listic limits of the typical high-purity smoothly, but must instead be renucleated A1„0„ targets prepared from starting or bypass that site. In either case, a powders furnished by three different higher stress would be required for vendors and fabricated by two different fracture. Independent evaluation of the techniques fell on a linear slope when scanning electron photomicrographs has plotted against target thickness (Fig. 9). favored this interpretation. Targets with finer grain sizes had V-, 's A working hypothesis'1' for the observed above this line. The material with the correlation between ballistic performance highest grain density (-0.099 grains/n2) and grain size can also be proposed from was prepared at LLL by hot pressing a a consideration of fracture mechanism. blend of 1% MgO-Al„03 powder at rela This hypothesis assumes the existence of tively low temperature (1475°C) (see a critical grain-density range, which im Fig. 10). MgO inhibited grain growth in parts to a material, a higher resistance A1203. to the propagation of a fracture. In addi The effect of microstructure on bal tion, there are three modes of fracture listic performance was also observed in to be considered; transgranular (across 5 AD-85 alumina andB4C Large differ the grain), Intergranular (along the grain ences in microstructure have been boundaries), and a transitional mode. observed in different lots of AD-85 armor The transitional mode of fracture is plates. Variation in the microstructure characterized by the activation of multiple modes of fracture, in contrast to the pre of B4C was noticed during dimension- * 5 dominantly singular modes of the other scaling studies. Thick B.C plates two types. It is proposed that the critical (>C25 in.) had a larger grain size, more grain-density range is coincident with the porosity, and poorer ballistic perform transitional mode of fracture or within the ance than thinner plates. Consistent transition zone defined in Figs. 5 and 6. scaling results could be obtained only by Support for this hypothesis comes from grinding all the B.C plates from the observations of the fracture mode of bal thickest plates used in these studies. listically tested targets, and the general Fracture Mechanism condition of the targets after ballistic tests. Early indications from examinations of A transition in fracture mode seemed to ballistically fractured surfaces with the occur when the grain density of the Be.B 2 scanning electron microscope were that targets approached 0.085 grains/ji . foreign particles altered crack propagation. The smooth fractured surfaces of the high- This hypothesis should not be confused purity Be.B targets contrasted sharply with the one previously put forward to explain the fracture of graded armor.5 with the rough fractured surfaces of the Experimental evidence to support the above 4 vol% BeO-Be4B targets (see Fig. 11). hypothesis has been collected on the single- phase Be4B targets while multiphase tar The BeO particles were located predomi gets are used for the crack blunting in nantly in the grain boundaries. It can be graded armor. -11- -i r Al Al 0 2 3 6061- .30-col / sharp T6 projectile- / / / / 1/4 / / / / / / / « - Fine-grain l%MgO-AI2C>3 a/ hot pressed at LRL / * - Fine-grain alumina / / A - Coarse-grain alumina, heat treated for 100 hr at 1900 °C / / D - Hot-pressed alumina / / o - Cold-pressed and sintered / alumina 2000 0.15 0.20 0.25 0.30 0.35 0.40 Thickness, A — in. Fig. 9. Ballistic limit versus thickness for Al„Og targets. -12. (see Fig. 12). In the transition region 3.-F i*. 'f 'J between these two size limits (0.04 to 0.12 grains//! ), the fracture bifurcates at grain boundaries and proceeds as multiple fractures (see Fig, 13a). The pathB of these multiple fractures are not predomi nantly transgranular or Intergranular. Their paths are Influenced by crystal orientation and aligned grain boundaries, the propagation preferring the paths of no** least resistance (see Fig. 13b). >-<. v- Electron microscope techniques were Fig. 10. Fine grained AI0O3 (~0.0P9 grains/ also used to examine debris from the H2) prepared by low temperature targets used to obtain the V , of points 1, (14?5°C) hot pressing of a fine Q powder blend (1% MgO-Al-Og). 2, and 5 In Fig. 6. Each point is in a different fracture zone. A general description of these techniques and the Metallographic examination of bal- features of Interest on the fractured sur listically fractured pieces of Be.B dis face of this debris are given In Appendix C. played predominantly transgranular Detailed examination of these fractured fracture for average grain densities less surfaces indicated that a higher stress than about 0.04 grains fa and predominantly was required to sustain fracture in the intergranular fracture for average grain transition zone (point No. 2 in Fig. 6) densities greater than about 0.12 grains/u than in the other two zones. The fractured o. High purity Be.B b. 4vol%BeO-Be4B Fig. 11. The typical difference in ballistically fractured surfaces of high purity (a) and doped (BeO) Be.B (b) as detected with the scanning electron microscope. -13- a. Transgranular fracture in a forget of b. Intergranular fracture in a target of average grain density <0.04 grains/u,' average grain density > 0,12 groins/V Fig. 12. The different modes of fracture in ballistically tested Be B targets with different grain sizes. 4 a. Fracture branches at grain boundary. b. Multiple fractures - Fig. 13. Multiple fractures in the transition region (~0.04-0.12 grains/^2) of hot-pressed Be4B powder (<20 diara). surfaces from the transition zone con Fig. 15) and intergranular (see Fig. 16) tained large amounts (>10% of surface) fracture zones. 9 10 The largest pieces recovered from the of hackle ' with nearly random orienta 3 In. diam targets with grain density in tion (see Fig. 14). Smoother fractured o surfaces with little hackle were observed the transition zone (0.04 to 0.12 grains//* ) for the predominantly transgranular (see are approximately 1/2 in. square and only o. Prepared on the scanning electron b. Prepared by r«pl!ca on an electron microscope. microscope. Fig. 14. Typical fracture patterns in the transition region (Fig. 6, point 2) for ballis- tically impacted Be.B targets. X) S i t ^r- I II M a. Prepared on the scanning electron b. Prepared by replica on an electron microscope. microscope. Fig. 15. Typical fracture patterns in the transgranular region (Fig. 6, point 1) for balUstically impacted Be4B targets. come from the edge of the targets. The generated from ballistic impact are Be.B with average grain densities outside described in the section on toxicity, these limits had larger (~1 in. diam) pieces There are several reasons that explain recovered from areas near the point of why the effect of grain size on the ballistic impact. Similar trends between ballistic performance of most ceramics is not performance and size and amount of debris always readily apparent. The mode of -15- a. Prepared an the scanning electron b. Prepared by replica on an electron microscope. microscope. Fig. 16. Typical fracture patterns in the Intergranular region (Fig. 6, point 3) for ballistically impacted Be.B targets. a. Indentation at > IO°ro slip plane b. Indentation parallel to slip plane Fig. 17. Effect of preferred orientation in Be4B on the KJioop microhardness indentations. fracture is not entirely governed by the or agglomerated impurities; and exces- grain size if the ceramic contains any of sive amounts (2-10 vol%) of grain orienta- the following features: relatively small tion (ratios 2-4:1, length to width), amounts (-1 to 5 vol%) of porosity; a sig- Usually one or more of these features nificant amount (>2 vol%) of finely dispersed shows up in all of the commercially man- impurities; small-amounts (<,2 vol%) of ufactured ceramics. This is especially relatively large (~>4 times the average true of most ceramics used for armor grain size) features such as large grains since tight specifications on high purity -16- and uniform microstructure are not main also affected the grain size of hot-pressed tained. beryllium borlde. The average grain The last feature (preferred orientation) dcnaity decreaaed with increasing temper was also observed In taking mlcrohardness ature for each powder (Fig. 20). Repeat readings on tetragonal Be.B. Slightly lower ing the hot-pressing procedure on the mlcrohardnesses were obtained when the same target also decreased the grain den longer dimension of the Knoop lndentor sity (Fig. 20). The decrease in grain was at an angle >10° to the most active density with increasing time at tempera slip plane (see Fig. 17a). No slip was ture and pressure is shown for 2 powders evident when the longer dimension was In Fig. 23. Insufficient pressure parallel tothe slip direction (see Fig. 17b). (<3000 pai) at processing temperature re Similar slip in many grains was observed sulted In lower density and higher poros after ballistic impacting Be.B targets ity. Porosity also inhibited grain growth. (see Fig. 18). Attempts to Increase the grain size of hot-pressed targets of Be4B and Be,B with Process Variables post-hoat treatments at various tempera The important property of grain size tures (800-1000°C) and times (8-18 hours) was found to be influenced by several —6 process variables. Microstructure was were unsuccessful. Vacuum (10 mm Hg) controlled primarily by the particle-size heat treatments caused growth inhibiting distribution of the starting powders and pores to form along grain boundaries. No the amount, nature and dispersion of im increase in grain growth or pore formation purities (Figs. 19 and 20). The particle- was observed during heat treatment in an size distribution ranges offered by two Inert atmosphere. vendors are shown in Figs. 21 and 22. Improvements in the VBL of reaction Two other fabrication parameters, hot-pressed Be.B were obtained by using temperature and time at temperature. process variables to manipulate the grain size ofthe targets (Fig. 6). The approaches a. 30 ca I project! le impact Fig. 18. Typical activation of slip planes by ballistic impact on Be4B targets. 17- —r—|—r—i—r—|—i—i—i—|—i—i—i—|—i—i—i—|—i—i—i— 0.16 :I : » ^/—Reaction hot-presied blends of Be B powders 0.14 1 \ - \ \ V : 0.12 ; k • 0.10 \ y~ Hot-pressed Be. B powders ^""""! I Y i 1 • \ \ 0.08 1 \ ? grai n de i X ff 0.06 \ 1 \ \ v 0.04 \ X \ 0.02 \ 0 -20 10-20 -37 20-37 -44 37- Particle Size Ronge — n sieve Fig. 19. Average grain density versus the particle size of the starting material for Be^B targets. -18- -i—i—l—I—i—i—r | » ' r | i i i—|—r i Ball ml Dad Ba. B powder 0.16 -,, \ Reaction ' " Hot-Pressed 0.14 _Blendi of Be and \ B powders \ A 0.12 V \ N *^. 0.10 "o Screened Be 0.08 . 4 Vol %B«0 — Be .B -8 \ * o \. (Repress) V V 2 0.06 \ V 0.04 4 Vol %Al20g — Be4B 0.02- 01 I l_ J_J I I I I I L 1000 1020 1040 1060 1080 1100 Hot pressing temperature — "C Fig. 20. The effect of the hot-pressing temperature on the average grain density of Be.B targets. -19- uu '' ' •"T" . 80 - - 60 - - Vendor fl I 40 - i i i.ma] i. i i i nut . Vendor *2 -* I 10 100 - Porricle diometer — ^ 20 — ^ * «—Vendor *1 Fig. 21. Typical particle-size distribution curves of Be^B powder from two 0 ,1 LLU vendors. 0.1 1 10 Particle diameter —n for increasing grain size were less suc Fig. 22. Typical particle-size distribution cessful on the reaction hot-pressed targets curves of Be2B powder from two than they had been on the targets hot- vendors. pressed from the pre-synthesized powders (Figs. 19, 20, and 23). very tight temperature control to avoid An average fine grain microstructure of melting. Longer hot pressing times <5 p in diam could be obtained under the (>30 min) seemed impractical in the light conditions listed in Table 2 if complete of the shape of the upper curve in Fig. 23. reaction between the Be and B powders Complete reaction of relatively large was achieved. Under these conditions particles ($44 u diam) could be achieved complete reaction was impossible if rel within 30 min at temperature and pres atively large Be particles f>20 ,u diam) sure. Without the applied pressure were present. This incomplete reaction (£3000 psi), no apparent grain growth was is apparent in Fig. 3 and is the primary detected. cause of decreasing grain density with Attempts to increase the grain size of increasing Be particle size (see upper reaction hot-pressed Be.B and Be„B tar curve of Fig. 19). While incomplete re gets by vacuum or inert atmosphere heat action resul in the formation of a cermet treatments produced the same results microstruc -e, the desired fine distribu obtained with hot-pressed targets. Voids tion of UK metal phase is difficult to con were formed in vacuum and no increases trol by tliis approach. in grain size were obtained with either A small decrease in average grain den heat treatment. sity was obtained by either increasing the The apparent resistance to grain growth hot-pressing temperature or time at tem- of reaction hot-pressed targets is in con ptrature during reaction hot-pressing trast to results obtained in hot-pressing. (Figs. 20 and 23). Higher temperatures This behavior can be attributed to higher (>1040°C) were impractical, requiring concentrations of fine BeO particles which -20- o.i6i—r - , _, , p— , p_ Reoction not-pressed blends of Be & B powders 0.14 0.12 a 0.10 I" 0.08 « Hot-pressed Be. B powder § 0.06 0.04 0.02 tr 20 30 40 50 60 Hot Pressing Time — min Fig. 23. The effect of the hot-pressing time on the average grain density cf Be^B targets. -21- the loaded die during the initial stages of hot pressing (<400°C). The use of BN powder in the slurry prevented the car bonization reactions at the interfaces. The B or BeBg slurries improved the hardness and salt water corrosion resist ance of the targets. Surfaces exposed to B or BeBg slurries during hot-pressing were proposed for use as Impact surfaces, while those exposed to BN slurries were proposed for the surface to be bonded to the backup plates. CAST TARGETS Fig. 24. Non-uniform Be B grain growth resulting from lon4 g exposure at hot-pressing temperature and Casting is generally an economical pressure. fabrication process for large-scale manufacturing. The relatively low liquidus temperature fen65°C) of Be4B inhibit grain growth during pressing. The (see Fig. A-l) prompted an investigation main sources of this contamination are of the casting behavior of this compound BeO present in the starting Be powder and and the ballistic performance of cast oxidation of this powder during reaction targets. hot-pressing. The total BeO content can According to the Be-B phase diagram vary from 1 to 6 vol%. (Fig. A-l), the cooling of a melt with a Long times f>30 min) at hot-pressing composition of 20 at.% B-Be from 21350°C temperatures and pressures increased will result in approximately 28% of the non-uniform grain growth as shown in melt forming Be„B between 13S0 and Fig. 24 and caused excessive formation 1165°C. The remaining melt should then of carbides at the interface between the form Be B at 1165°C. This peritectlc graphite die and the target. The non 4 behavior of Be.B was not observed when uniform grain growth was reduced by wet melts were rapidly cooled (£lO°C/sec) ball milling which improved the blend mix. between 1350 and 1165°C. Only an insig Inter facial reactions were reduced by the nificant amount of (<5 vol%) Be„B was inexpensive method of lining the graphite formed. dies and punches before hot pressing. A slurry made of fine powder (BN, B, or Attempts to prepare Be.B targets by BeBn> mixed with alcohol and a wax binder melting and furnace cooling resulted in was painted or sprayed on the inside sur targets containing shrinkage cracks, vary faces of the die and on the surface of the ing amounts of porosity, and large grains. punches exposed to the Be-B blends. The Two commercial techniques, chill casting wax binder and alcohol were baked out of and hot topping, were used to get dense targets of two compositions, 12.5 and -22^ 30.0 at.% Be-B. The low ballistic per (1) molten Be^B does not wet or infiltrate formance (50% of hot-pressed 12.5 and porous BeO surfaces, (2) porous BeO acta 20.0 at.% B-Be) of these targets was as an insulator and prevents cooling of the attributed to their microstructures. These Be^B from the side walls, and (3) the liner targets contained large columnar grains prevents cracking of the crucible, absorb' which were mostly oriented parallel to the ing the pressure which results from the path of the projectile. As expected, the difference in expansion coefficients between mode of fracture was predominantly inter- the BeO crucible and the solidifying Be.B. granular with this grain orientation. The liner was prepared by hand packing BeO powder (<5 u diam) in a graphite Directional Solidification mold and sintering at 1300oC for Two alternate casting techniques were I hour. tried in the hope of improving mlcrostruc- The Be.B fragments were heated in ture and with it ballistic performance. this apparatus to -800°C in vacuum. The Directional solidification to orient the vacuum chamber was filled with argon columnar grains perpendicular to the path and the Be.B was melted and was held at of the projectile was one of the approaches. 1300°C for i hour. The crucible was then Two methods of preparing directionally lowered about 2 in. onto a copper chill solidified targets were investigated. In block. After another 10 mln, the temper the first instance, molten Be.B was poured ature of the heating element was gradually into hot BN molds and the melt cooled from reduced to room temperature. In this the bottom. The BN molds reacted with manner directional solidification parallel the molten Be4B (1400°C) when the molds to the liner surface was obtained. This were preheated to temperatures of 1180, technique also yielded a slightly finer, 1150, or n00°C. The reaction with BN more uniform grain structure than ob occurred even though the BN molds had tained with BN molds (Pig. 25b). been vacuum degassed at temperatures The directionally solidified targets had above 1400°C. Plates with marginal relatively fine columnar grains that were densities (597%) were obtained by grinding perpendicular to the path of the projectile off the reacted layers (see Fig. 25a). (Fig. 25). The ballistic performance of The second method consisted of cooling these targets was 35% higher than the first the bottom of a BeO crucible containing Be4B castings but still -30% below the molten Be.B. Bottom cooling was accom performance of hot-pressed Be4B. The plished by use of a top loading vacuum fur mode of fracture of the cast targets was nace with a cylindrical tungsten mesh predominantly transgranular. These heating element. Be.B fragments from results suggested that finer grain size previous ballistic tests were placed in the might improve ballistic performance. crucible (4 in. diam, 7 in. high) and The practical problem of removing suspended by a molybdenum wire into the porosity while maintaining unidirectional heating element. The crucible was lined orientation hampered any further reduction with a porous (80% porous) BeO layer of the grain size by the above casting (£« in. thick) for the following reasons: techniques. -23- Direction of Projectile Molten Be .B poured Into hot b. Be^B malted in BeO crucible BN molds and cooled from the and cooled from the bottom. bottom. Fig. 25. Typical fine columnar grain structure of Be^B targets fabricated by unidirec tional solidification from the melt. These targets have been ballistically tested. Grain Nucleation The second general approach involved increasing the number oi nucleation sites and decreasing grain growth in order to obtain a fine, randomly oriented grain structure similar to that found for hot- pressed Be.B. A casting with these prop erties was achieved by employing the following techniques: doping with BeO to provide grain hucleation sites; ultrasonic vibration to stimulate nucleation; vacuum casting to prevent gas bubble voids; and rapid cooling to prevent grain growth. Experimentally, Be.B containing 4 vol% of small particle (<1 ti diam) BeO was heated by induction in vacuum to -S00°C before melting under a partial pressure of Fig. 26. Typical fine random grain struc argon (-3/4 atm). The Be^B melt was ture obtained by ultrasonically cgitated to keep the BeO particles suspended vibrating the melt (4 vol% BeO- Be4B) to stimulate grain nuclea by coupling on the melt instead of using a tion during vacuum chill-casting. -24- susceptor. The melt was rapidly quenched While promising specimens i~l/Z in. by lowering the crucible three-fourths of diam) were prepared with this casting the way into an ultrasonically vibrated procedure, targets large enough to bal- bath. The ultrasonic agitation stimulated listlcally test (23 in. diam) were not pos grain nucleation at prominent sites (BeO sible because of the size limitations of particles, impurities, etc.) and the ultra the existing equipment. We believe that sonic bath cooled the melt rapidly to pre the ballistic performance of cast Be.B vent grain growth. The cast Be^B disk targets would be comparable to that found was dense with a fine random-oriented for hot-pressed Be.B targets, provided grain structure (see Fig. 26). the mlcrostructures were similar. The Ballistic Performance of Metal-Graded or Reinforced Beryllium Boride Armor Improvements in the ballistic perform the excellent ability of the metal phase to ance of ceramic armor can be achieved "wet" the TiC. This "wetting" behavior by finding the proper balance between produces a continuous, uniformly dispersed compressive strength and ductility in network of metal between TiC grains with 9- 5 relatively low amounts (<20 vol%) of metal. tension. Part of the high compressive Similar interaction between low density strength of the ceramics can be traded for (<3 g/cc) ceramics and metals should be ductility to delay failure in tension. Since sought for light armor applications. the impact surface of the armor needs a Wetting studies can be used to screen high compressive strength to defeat the 11 12 metal candidates for cermets. ' point of the projectile, the ideal solution A few attempts to obtain cermets with would be to grade the amount of ductility the more promising ceramic armors through the thickness of the armor with s - -v. I 3000 . JT^ 1 • u s / LRL .30-col . / sharp "*"•—6061-T6 a luminum - 1 • / projectile —«* I 2500 < f 0.25 in. -•- — «• U-0.25 in. - . 1 . 1 1 . _ 1 1 1 1 10 15 20 25 30 35 40 Metal (Ni, Mo) —vol Fig. 27. Ballistic limit versus metal content for TIC cermets. Be4B-Be The graded-metal portion of the target shown in Fig. 28a was prepared from Be Controlled solid state diffusion provided and Be.B powder blends while the metal- an alternative technique to TiC-(Nl, Mo) containing portion shown in Fig. 28b was 4 type wetting, producing a chemical bond obtained with Be honeycomb sheets and with no brittle interface. The interfacial Be.B powder. Four more series of bal bond between the Be and Be.B was as listic targets were prepared by these two 4 methods in order to evaluate higher metal strong as the parent materials. Residual loadings and different geometries. stresses at the interface were low since Both methods yielded graded-metal all expansion coefficients were close. No targets with higher VB,'s (4-8%) than hot- brittle interfacial layer was formeo between pressed Be.B targets, but values lower Be and Be4B since no other compounds than found for earlier Be4B-Be graded exist between these compositions according targets. The powder blended series with to the phase diagram (see Fig. A-1). Two the highest (58 vol% Be) metal loading methods of preparing the Be B-Be graded 4 (see Fig. 29a) had the same ballistic per armor were described earlier (cross formance as hot-pressed Be4B targets. Bections shown in Fig. 28). These initial By reducing this metal content (32 vol% Be) Be B-Be graded targets had significantly 4 in the other powder blended series (see higher V 's (a 10% on an areal density BL Fig. 29b), the ballistic performance was basis) than hot-pressed Be4B targets. 26, Direction of Projectile Be.B Five layers of Be >Vol% Be-Be B honeycomb filled 4 ^^^^^^K^ witwi h Be.B to get an overall composition of JBockupNatTyi °]J Mvol%Be-Be4B. Epoxy bonded inter V Epoxy bonded inter face (1 mil) face O mil) Fig. 28. Schematic diagram of early Be.B-Be graded targets. Direction of Projectile I Be4B Be4B 11 vol %Be-Be^B 11 vol %Be-Bo4B 58 vol %Be-Be,B 32 Vol %Be-Be4B \ Backup Plate A Backup Plate -Epoxy bonded interface ( 1 mil) -Epoxy bonded interface (1 mil) b. Fig. 29. Schematic diagram of Be.B-Be graded targets prepared from powder blends. increased to 8% above hot-pressed Be.B formance was not higher than Be.B even targets. The relatively large grain-size with complete bonding along the Be sheet range in the Be rich layers of these tar interface and obvious diversion of the gets undoubtedly had some detrimental fracture by the Be sheets (see Fig. 32). effect on their ballistic performance (see Ballistic performance was improved to Fig. 30). 4% above the level found for Be.B targets Graded targets prepared from alter by replacing the eight layers of Be sheet nate layers of Be sheets (50 vol% Be) and (10 mils) with one thin layer (-10 mils) of Be.B powder also were found to be equal blended powders (32 vol% Be-Be.B) and in ballistic performance to hot-pressed two Be sheets (S mils each) (Fig. 31b). Be.B targets (see Fig. 31a). Their per The excellent bond between these layers -27 Direction of Projectile 1 | H vol % Be-B* B ' 4 . -..i/S pM volS.Be-Be.B' .32 vol % B.-Be.Bi I 120 n Fig. 30. Microstructure of the interface between the two Be rich layers of the Be.B-Be graded targets prepared from powder blends (see Fig. 29). * Direction of Projectile Be4B Alternate layers of Be sheets (10 mils -32 vol %Be-Be4B thick) and Be^B; VM^f'/nmr EZZZ222ZZ22 • Two Be sheets • 50 vol % Be-Be.B (5 mils thick) Backup Plate Epoxy bonded inter s • Epoxy bonded inter face (1 mil) face (I mil) Fig. 31. Schematic diagram of Be^B-Be graded targets containing Be sheets. after hot-pressing is apparent from the Be.B-Be graded system for this in Fig. 33. This figure also shows that a vestigation are as follows: crack initiated in the Be.B during ballistic • demonstrated improvement in bal impact was stopped (crack blunting) in the listic performance with certain graded first Be sheet. compositions and geometries. We believe a systematic investigation • relatively low fabrication temper into the effect of relative amounts and atures (<1100'C>, dispersions of metal in the graded armor • simplicity of fabricating various would be valuable. The reasons for using graded compositions and geometries. -28- Direction of Projectile -*"*. / Fig. 32. Microstructure of the alternate 1 ' 'I layers of Be sheets (10 mils) and Be«B hot-pressed powder region of Be4B-Be graded targets (see •M^B^B^ Fig, 31a). gleih—t(5wil»)| • and superior ballistic performance Fig. 33. Microstructure of the hot-press to any known light weight armor. bonded layers of target shown in Fig. 31b. Note that the crack initiated in the Be4B during bal Be.B-N4 i OR Ni BASED ALLOY listic impact was stopped in the first Be sheet. Preliminary investigation of Be.B-Ni graded systems were made because of the layer formed between the metals and Be.B jTood ductility of Ni and the possible chem was not much harder (20-30%) than the ical compatibility of Ni and Be.B at the Be.B. The lower ballistic performances fabrication temperature (<1100*C) of Be.B. of these two graded series (24 and 81i, It fas also hoped that the high ductility of respectively as compared to Be.B on an Ni \greater than Be) would improve the areal density basis) was attributed to the cracir blunting behavior. However, the brittle fracture along the interface layers relatively high density of Ni (8.9 g/cc) does between the metal and Be^B (see Fig. 35). not male* it a very likely candidate for In anticipation of experiments with the light armor applications. Early results Ni system, preliminary studies were made also showed that Ni was not completely into the possibility of pressure bonding stable in the presence of Be.B at the Ni to aluminum backup plates. It was fabrication temperatures. Nevertheless, thought that a ductile bond at this interface ballistic tests «*f Ni-Be.B and nichrome would improve ballistic performance and wire-Be.B targets (Fig. 34) were prepared multi-hit capability. Good metallurgical since the microhardness of the interface bonds were obtained at the Ni-Al interface 29- Direction of ProjteriU 8*43 -38vol %Ni-B«.B 20 vol %nichfomt (lOmilj) 4 wir«- Bt,B (50mill) wuhhuhmi -Nifoil (5 mid) B«4B(30mili) Backup Plate • Epoxy bondtd inlar- \ *~ Epoxy bonded inUr- foct (I mil) \_face(1mil> "Aluminum alloy (606I-T6) Aluminum alley (6061-T6) Fig. 34. Schematic diagram of Be^B-Ni and nichrome graded targets. Direction of Projectile with an applied pressure of 1000 pst at 450*0 for 20 mln or 500'C for 5 min. The mlcrohardness of this interfacial layer (400 kg/mm) was higher than the Ni (200 kg/mm) or Al alloy (180 kg/mm). This bond was not balllstlcally lusted since the studies or. the Bc^B-Ni graded targets were discontinued after the brittle interfaces between B04B and Ni failed during ballistic tests. Wc believe that the pressure bonding technique should be applied to the more successful graded targets, especially Be4B-Bc. The Be surface of a Be4B-Bc graded srmor plate Fig. 35. Brittle fracture along the inter could be bonded to a metal backup face layer of a balltstically plates to improve ballistic performance impacted Be4B target reinforced with nichrome wires. and multi-hit capability. Toxicity Studies A proposal advocating the fabrication toxicities of compounds that might be used and use of beryllium containing compounds in the fabrication of the beryllium borldes must include a toxicity study. The (i.e. HeS04, Be(OH)2, BeO, beryllium -30- powder) arc known and these materials exposures. These studies are being done are presently handled on a production with Be .B, Be„B, and BeBG debris as scale at many plants. The preparation of well as commercially available Be.B and the beryllium borldc powders or blends of Bo„B powders. Inconclusive results were Be and B powders for hot pressing or obtained after the first 6 months period. casting of Bc,B can be handled simi Experiments over 6, 12, and 18-month larly. ' However, little Information periods are in progress. A separate was available on the tonicity of the beryl report will be prepared when all of these lium borlde powders themselves. Such results are available. Information could only simplify the pro Should an unusually high toxicity potential cedures used In the handling of these for debris be established by the above powders. toxicity studies. Information about the Previous studies concerned with the amount and size of this debris would also use of beryllium in armor have concluded be required to determine the potential that, "Based on the information provided, hazards involved in specific armor appli the risk of increased morbidity due to the cations. A method of obtaining this in use of beryllium containing armor 13 con formation was developed at LLL. This sidered negligible from the viewpoint of method was designed to collect the maxi inhalation of respirable particles or con mum amount of debris generated during tamination of soft tissue wounds." Al ballistic impact. In most light armor though the preceding statement could in systems significant spall suppression clude the beryllium borides, additional (£400% suppression ) is obtained with information was desired in two areas: spall shields. This factor was not taken (1) the effect of direct exposure to the into account in our work. The signifi blood through open wounds and tc the cance of this type of suppression can be lungs by Inhalation of fine debris; and estimated later for specific applications (2) the amount and size distribution of if the general efficiency of ihe specific beryllium borlde debris generated by a spall shield is known. The toxicity of ballistic impact. most inhaled powders depends on the foi ls The toxicity of both the beryllium lowing interrelated variable factors ': boride powders used in the fabrication of targets and the debris from targets it 1. the physical and chemical properties, currently being investigated by the Depart of the powder, ment of Health, Education and Welfare 2. the quantity of debris deposited in (HEW> in Cincinnati, Ohio. The toxicity the airways and the lungs, studies at HEW are being performed by 3. the relative solubility of the debris intratracheal injection of beryllium boride in the tissue fluids, particles (*5 p diam) in the lung tissues 4. and retention and release of the of rats. This technique was selected powder. because it provides information relating Considering only the density (~2 g/cc) to the effect that these particles might of the beryllium borides, particles of have upon lung inhalation and open wound approximately >5 ,u diam would deposit in -31 1001 1 1—i i i i 111 r- i—rrrm 00 S 60 % 40 20 100 10,000 Particle diom»t»r — \i Fig. 36. Typical size-distribution curves of all the debris collected from the Impact aide of ballistically fractured beryllium boride targets. the airways, and particles of approxi All the size distribution curves of lh« mately £1 ix diam would not be retained in beryllium boride debris collected from the lungs. 17 As indicated above, chemical factors also influence the particle size range that can be deposited in the lungs. For the present investigations it was assumed that particle retention in the lungs would be in the diameter range of 1 to 5 p. The particle size limit of major interest as far as contamination of wounds is con cerned was considered to be S45 tt diam. Larger particles have a lower chemical activity (less surface per wt unit) and are relatively easy to remove. When the particle size limits of major interest, 1 to s and £45 M diam, had been defined, techniques were incorporated into 1 5 10 SO 100 the existing ballistic testing procedures to ParticU diamttttr — \i collect and characterize these particles. A Fig. 37. Size-distribution curves of <4Su description of the collection and characteri diam debris collected from the impact side or ballistically zation techniques used .or the ballistically fractured beryllium boride tar generated debris is given in Appendix D. gets, -32' 100 I // • 80 - /I - | 60 - /I - 5 / / 40 / / • s / * 20 - / - - ' 1 — 10 too 1000 10,000 Panicle diameter — \t Pig. 38. Size-distribution curves of all the debris collected from the back side of bal- Ustically penetrated beryllium borlde targets. the impact side of the targets Uy between the two curves shown in Fig. 36. Sire distribution curves of the debris in the most Interesting portion (<45 >i diam) of these curves are shown in Fig. 37. Com parable boundary distribution curves for the debris collected from the back side of # ball 1st icaUy penetrated targets are shown in Figt. 38 and 39. The debris collected in front of targets was characterized only when the Impact velocity was near (£5%) the VQL of that target. The debr's collected from the backside of penetrated targets was characterized only when the Porricle dioffieter — (i target was impacted slightly above (SI 20 ft/sec) the V . These Impact Pig. 39. Size-distribution curves of <45p RL diam debris collected from the velc-city limitations reduced the Influence back side of balKstically pene- of impact and exit velocity to the range of traded beryllium borlde tar gets. greatest interest; near the VBL. .33. The most pertinent information ob fracture theory described in a prior tained from these size-distribution curves section. The amount of fine debris should was the correlation between debris size also increase with increasing VQ, . The Finer particles were generated amounts of the two most interesting size and VBL * from targets with higher V„L's. This fractions (<5 and <45 u dfam) are plotted correlation was also proposed from the against V„L in Figs. 40 and 41 for debris 2700 T 2600 2500 < 45p diom j- u A 2300 2200 2100 I 10 12 OtbrU < 5 |i diom I 10 20 30 40 50 60 Owfi'i < 45v diam Wtighr of dtferit — mg Fig. 40. Quantity of beryllium borlde debris collected from the impact side of targets versus ballistic limit. -34- 5 Debris < 5 (» dfom 10 20 30 40 50 I I I ' • i i L_ Debrii < 45 |i diom Weight of dabrls — mg Fig. 41. Quantity of beryllium boride debris collected from the back side of penetrated targets versus the exit velocity of the projectile. •35- collected in front and behind the targets, (P.H.)WorI=^(l-SS)(TF)Wor, respectively. These results are also consistent with the fracture theory: the amount of debris increases with in Symbol Description P.H. = Potential hazard creasing VBL (Fig. 40). The number of <5 \i diam particles W = Wound exposure (<45 p diam generated on the Impact side of the tar debris) get increases at a greater rate with in I = Inhalation exposure (<5>i diam creasing VB, than does the number of debris) <45 u diam particles (see Fig. 40). Con versely the quantity of <45 \x diam O = Amount of debris fag) particles generated on the back side of V = Volume into which debris is dia- 3 the target increases at a greater rate sipated (m ) with Increasing exit velocity than does the number of <5 \i particles (see Fig. 41). SS --• Spall shield efficiency (constant A first approximation of the potential SI) hazard from this debris for a specific TF = Toxicity factor established from armor application might be calculated toxicity studies (In progress at from equations like the following: HEW). Environmental Tests The behavior of beryllium borldes in were reduced to -0.01 to 0.9% by vacuun likely fabrication and application environ drying the exposed powders. X-ray dif ments was studied in order to better fraction results showed no shift (<1%) in assess potential uses. the original compositions. Fabrication (hot-pressing or casting) An indication of the maximum oxidation environments could give rise to the fol rate of Be.B and BegB powders (-400 lowing problems: the adsorption and sur mesh) in air at elevated temperatures was face reaction of moisture with starting obtained by thermogravlmetrlc analyses powders and finished products, and the (TGA). The Be.B powder was observed oxidation and carbonization of the com not to gain weight until the temperature pounds at elevated temperatures. Expo reached 410°C (see Fig. 42). After a sure to moisture during handling and 30-hr exposure at this temperature, the storage had little or no adverse effect on rate of weight gain had decreased from the Be.B or Be.B powders. Fine powders -0.1%/hr to 0.02%/hr. The latter rate (-400 mesh) with large surface areas was maintained even after the temperature (-2 m*/g) from two different endors were was increased to 506°C. The tests were exposed to distilled (75 and 100% humidity) terminated when the weight gain exceeded and salt water (95% humidity) atmospheres 4%, since oxidation above this level was for 104 days. Weight gains of 0.02 to 1.3% considered undesirable. According to 36 506 ± 5°C a? 3 I 8> J 2 Moisture removed during vacuum drying 2 410±5°C -1 _L J_ I _L 20 40 60 80 100 120 140 160 180 Time at temperature — hr Fig. 42. Weight gain of Be^B powder at elevated temperature In air. x-ray diffraction results, this weight gain and Be„B powders during hot-pressing. was due to the formation of BeO. Similar No significant Increase In BeO content results were obtained (see Fig. 43) for WBB detected by x-ray diffraction techniques Be2B powder. However, significantly when the Be^B, Be2B, or B-Be blended lower rates of weight gain (0.013 and powders were hot pressed In graphite dies 0.005%,far) at the same temperatures and cooled to <400°C before removal from (410 and 506°C, respectively) were the dies. A Be^B disk (3 in. dlam, observed. 0.32 in. thick) showed a significant in The above results indicate the desir crease in BeO content (-6%), as compared ability of a protective atmosphere when with the starting powder (~3% BeO), when these finely powdered compounds are the disk was extracted from the die at consolidated at elevated temperatures ~800'C and air cooled. Extraction of the (>400°C). Casting operations with Be.B hot (>400°C) disks into a protective would also benefit from a vacuum or Inert atmosphere (or carbon black) would be atmosphere. The self-generated re required to reduce this surface oxidation. ducing atmosphere of graphite dies and Hot extraction of a disk this size (3 in. punches Is sufficient protection for the dlam) did not reduce its ballistic perform consolidation of the Be-B blends or Be.B ance which Indicates good thermal shock -37- 6 1 1 < 1 1 1 1 1 < 1 1 1 1 1 | l ~* 5 - ^^^""SOO* 5°C - 8, 3 1.1,1 . c ao y— Moisture removed during vacuum drying "•s6 2 - 1 - / ^ 41*0 ± 5 °C 0 - 1 1,1.1,1.1,1,1 1 • 0 50 100 150 200 250 300 350 400 450 Time ot temperature — hr Fig. 43. Weight gain of Be2B powder at elevated temperature in air. resistance. The shock resistance would reacting the carbide surface with water allow a faster hot-pressing cycling and and wasting away the products; or by more efficient use of the hot-pressing lining the casting molds with BeO. Lining facilities. the graphite dies with a thin layer (<-2 mils) Slight carbonization of Be4B and Be»B of boron or Be«B powder not only reduced to form Be,C has been observed under the amount of Be2C formed but also in three conditions: (1) hot-pressing Be^B creased the hardness and corrosion and Be2B powder in graphite dies, (2) re resistance of the target surface. action hot-pressing Be-B powder blends in Ceramic armors are exposed to numer graphite dies, and (3) chill-casting Be4B in ous environmental conditions as a result of graphite molds. In the first two conditions their various applications. To determine partial surface carbonization (<2 mils) the effect of all these conditions on the occurred after prolonged (>30 min) hot- beryllium borides is beyond the scope of pressing at 1075°C for Be4B and 1100°C this program. Some general observations for Be,B. Similar carbonization was and tests have been made to provide guidance obtained on Be.B surfaces exposed to the in determining the viability of these bordies graphite mold while chill-casting Be4B in certain environments. plates (4 X 5 X 0.4 in.) from 1300"C. These The excellent corrosion resistance of thin contaminated surfaces have no apparent borides with boron contents above 66 at.% effect on the ballistic performance of these (BeBg) is apparent from their insolubility materials. Beryllium carbide (Be„C) is in acids. ' This resistance is not easily hydrolyzed in moist air giving found for Be.B and Be^B, which are the 14 most attractive compounds for light armor methane. This surface contamination applications. The chemical stability of was eliminated by employing one of the these beryllium-rich compounds (233.3 at.% following procedures: lining the hot-press B) decreases with decreasing boron dies with a BN slurry coating; grinding content. the surface (~2 mils) of the component; 38- Direct ton of impinging stream Fig. 44. Profile views of surfaces of Be„B eroded by a 20-mil-diam stream of salt water. A severe test for water damage was thermal-shock conditions has already made by directing a stream of distilled or been mentioned in regard to hot extraction salt water at the surface of Be.B or Be„B of hot-pres»ed disks.. This same behavior targets. A pressure of 30 psig was main was observed in the temperature range of tained on a 20-mils-diam nozzle to form a +150 to -320°F. No degradation of boride single stream. The nozzle was perpen disks (3 in. diam, 0.32 in. thick) was dicular to and l,*2 in. away from the boride detected after they were heated to 150*F surface. Tl.e recycling bath temperature and quenched in liquid nitrogen. Larger was 105°F. No erosion or weight change disks (6 in. diam) were also subjected to was observed with distilled water imping similar thermal shock tests and showed ing on Be.B or Be,B after 3SO hrs. no degradation. Severe erosion and weight loss of the Be^B A simple test to qualitatively determine and Be,B surfaces were apparent with salt shock resistance and thermal conductivity water after 32 hrs exposure (see Fig. 44). of the beryllium boride targets was per These surfaces can be protected from formed on Be4B, Be2B, BeB2, and BeBg direct erosion by salt water by installing disks. The centers of the boride disks spall shields or by providing a thin surface (3 in. diam, 3 in. thick) were rapidly layer of high boron content (BeB, or BeBg). heated with an oxygen-acetylene torch to Such a surface layer can be obtained by the their melting points and air cooled. Be.B, use of B or BeB2 in slurries used to coat BegB, and BeB2 showed no spalling or the pressing die and punches. cracking. The relatively lower thermal The excellent behavior of Be^S and conductivity of BeBg caused it to behave Be2B under high-temperature (£800*C) as do most ceramics (i.e. B4C Al2<>3, -39- and A1B,2) under these conditions: it quantitative studies vrould be needed to immediately spoiled at the point of contact establish the value of these materials with the flame. in severe environments, they show The oxide Summary The potential of beryllium boride for Mlcroatructure has been shown to be a use as light-weight armor is apparent critical performance factor. A direct from its ballistic performance. Its use correlation betweer grain size and bal however will probably rest on economic listic performance can be drawn and then factors. Be.B and Be^B armor is very related to the mechanism of fracture. easy to fabricate. This is in contrast to Fracture can occur transgranularly, other ceramic armor systems where intergranularly, or by a transitional economical approaches to fabrication »r« mechanism. The transitional mode is not available due to the refractory nature operative for a particular range of grain of most ceramics. The combination of sizes. When transitional fracture occurs, superior ballistic performance and low it results in the ballistic limit being higher fabrication temperature make the beryllium than the limits found with the other fracture borides the most outstanding candidates modes. Grain sice can be influenced by for advanced light armor applications. process variables such as temperature, Hot-pressing, reaction hot-pressing, and pressure, and the composition of the casting all appear to be practical processes starting materials. for fabrication. Inexpensive techniques for The excellent thermal shock and spall increasing thehardness and corrosion re resistance of Be.B and Be.B in combina sistance of hot- pressed surfaces were found. tion with its likely oxidation resistance The low temperature of fabrication suggests multipurpose applications. On allows the addition of metals to the the negative side, erosion of these mate ceramic to form graded armors. The rials was observed when a jet of salt water performance of metal-graded armors was impinged on their surfaces for several was improved by varying the amount and hours. Under these conditions, a spall location of the metal phase. Beryllium shield or higher boride surface layer boride-nickel graded targets failed be would be required to prevent this erosion. cause of the detrimental effect of the Toxicity studies are currently under brittle interface between the ceramic and way at HEW laboratories in Cinnciimati, the metal. Ohio. We have developed a method for Our results have also brought perform assessing the amount and size of debris ance parameters into sharper focus. generated by ballistic impact. There -40- exists a good relationship between the and the backup plate, and compressive- ballistic limit of a material and the reinforced loading of the ceramic with character of its debri3. surface coatings, metal fibers, wires or For the future, the most promising sheets. way of Improving the ballistic perform Lastly, we believe that the initial coat ance of beryllium borides seems to lie of raw materials couM be operationally in the use of the graded armor concept. offset by recycling the waste, broken and The goals in this area should include: obsolete »rmor plates, and that the long increased ductility of the -ceramic, in term coat would be similar to other creased bonding between the ceramic ceramic armors. Acknowledgments The work of the following people is Department of Health, Education and acknowledged: Valuable guidance on the Welfare Laboratories in Cincinnati, Ohio. fracture behavior and penetration mech William Kuhl performed most of the cor anics of materials was obtained from rosion studies and fabricated many of the Mark Wilkins. Professor Van Frechette ballistic te.it specimens. William Gust of Alfred University guided the evaluation did the equatlon-of-state measurements. and interpretation of ballistlcally fractured Charles Honodel, John O'Conner, and materials. Lester D. Schesl and Herbert Nate Rawla performed the ballistic experi E. StoV.inger investigated the toxicity of ments. Alan Ulricli prepared the mate the beryllium boride powders at the rials for microscopy studies. -41- Appendix A: Preparation of Materials and Analytical Evaluation The Be-rich side of the working Be-B tlon of the beryllium borlae compounds by phase diagram was followed in the prepara- reaction hot-pressing (see Fig. A-1). 2200 Fig. A-1. Rough estimate of the beryllium-boron phase diagram (prepared by Gordon Godfrey and Van Frechette at ORNL in 1968). -42- The two phases of primary interest, Several analytical techniques were used Be4B(6) and BCjBfa), were prepared by in the evaluation of these compounds. reacting Be and B powder blends below Total Be and B contents were analyzed by 19 20 their liquidus temperatures (~U10°C and wet chemical methods, * trace im -1165*C, respectively). According to purities by emission spectroscopy, and Fig. A-1, attempts to prepare these total oxygen content by vacuum fusion pi compounds from a melt would result in analysis. Phase identification and the formation of a two-phase material, quantitative phase analyses of BeO were since both Be.B and Be„B decompose accomplished by x-ray diffraction. below their melting points (~1165°C and Quantitative analyses by x-ray diffraction -1370'C, respectively). The low melting of BeO in the as-received beryllium boride point of the Be4B does suggest the pos powders required standards of fine sibility of preparing a two-phase (~30 vol% (<5 it diam), low-fired (<1200°C) BeO Be2B-Be.B) armor material by casting. particles uniformly dispersed in htgh- Preliminary evaluation of casting was purlty beryllium boride powder (-400 mesh). reported In Ref. 5 and was continued in a Analyses of hot-pressed beryllium previous section of this report. boride. Table A-1. Typical analyses of Be.B and 3e2B powders (-400 mesh) from two vendors. Vacuum Analysis Wet chemistry b Be4B A Vendor 97 1 2 (Hell 6) LLL 75.2 20.2 S 3.1 w:% T 2.04 0.10 O.OS Be.Bb B Vendor S T LLL 74.5 22.9 S T T 2.02 0.22 0.02 Be»B A Vendor 10 85 2.5 2.5 M S T T (Heat 16) LLL M s 7.7 wt% 3.18 0.18 0.01 BCnB B Vendor T s (Lot1832) LLL 58.7 34.9 s T b Vendor T Be2B B s (Lot 2135) LLL 5G.1 35.9 5.0 wR4 M s 3.19 0.64 0.C *T—trice; S—strong; M—medium. °See T»b!e A-2. Table A-2. Spectrochemical analysis of Be.B and Be„B from two vendors. Spectrochemical analysis at LLL (ppm) Po*Uep type Fe Mg At SI O Nl Mn Zn Ca Cu Ti Co Sn Ag Sr Others Be.B A 5,000- 1000 500 500 600 500 400 £300 300 300 20 40 20 £5 <6 -60 (Heal C) 10,000 Be.B (Lci*213U B 1,500 2000 1500 1000 80 100 250 £300 150 150 150 £6 <6 •:•> C 43- parts required that the standards had a analyzed in Table A-l. The weight per similar hot-pressing history. cent BcO was reported In Ul.l.'s x-ray The Be4B and Be2B powders (-400 mesh) diffraction results. were supplied by two vendors for evalua The only limitation on the impurities tion. The Impurities varied slightly with listed in Table A-2 to be met by the each batch at the beginning of these pro vendora was that no trace of these im grams, since these compounds were not purities show up in the x-ray diffraction routinely produced by any vendor. Typical analyses. The suppliers are capable of analyses of these powders from suppliers providing lower impurity levels in the are listed in Tables A-l and A-2, The wet future if desired. chemical results from one vendor were The properties of the beryllium-boron reported as compounds (Be.B, Bc,B, and compounds that -vere reported in Ucf. 5 BeO), while the LLL results were re are also listed in Tables A-3 and A-4 ported according to the element (Be or B) along with more recent data. Table A-3. Properties of beryllium borlde compounds (Ref. 6). Theoretical Melting density Crystal point Hardness 3 Compound p°(g/cm ) structure CO (HK100) Be4B 1.94 Tetragonal -1160 1370 Be2B 1.89 Cubic -1500 -1300 BeB2 2.42 Hexagonal 3180 BeB6 2.35 Tetragonal 2020-2120 -3500 BeB18 2.42 Hexagonal — — Table A-4. Measured elastic properties of beryllium compounds (Ref. 6). Longitudinal Shear wave Bulk Shear Yield Density, sound speed, velocity, Elastic modulus, modulus, strength impedance K Y° Compound TiBe12 2.28 1.14 0.750 2.60 1.23 1.28 0.045 b Bs4B 1.94 1.275 0.838 2.45 1.32 1.35 0.058 b Be2B 2.03 1.27 0.800 2.58 1.52 1.30 0.057 BeB2 2.25° 1.28 0.828 2.88 1.63 1.54 — BeB6 2.31 0.135 Brush-thermalox grade BeO. The fabricated density includes contributions from BeO and BeB, impurities and from some porosity. Cr>nsity is lower than the theoretical density (p° = 2.42) because of a small amount of Be2B. -44- Appendix B: Average Grain-Site Determination The average grain size was deter ful in evaluating the effect of grain mined by the Heyn'B intercept method.7 size on ballistic performance cf a Thla mcthou was selected becauae the material. grains wero not equiaxed (width/length A leas accommodating error is ratio * 0.8). Introduced in this method of determining The average grain size was deter average grain size when the range of mined by counting line Intercepts in two grain else Is large (greater than s factor directions; parallel and perpendicular to of -3). Since the mode of fracture is the hot-pressing axis. The intercepts on affected by grain size and grain boundaries, two lines In each of these directions were the ballistic performance of two ceramics counted on four typical microatructural with the same composition and average views. The mlcrostructurc was magnified grain size can still be different If the on a metailograph until approximately 20 grain sire ranges are not similar. Sev lntercepts/70.7 mm were obtained. The eral available methods of calculating the average number of grains/mm in both average grain size might adjust this directions was multiplied together to get average to more closely represent the the number of gralns/nm2 or converted behavior of the fracture. Due to the to grains/{i . complex nature of fracture In a poly- These grain-size counts are too high crystalline material with a large range by a factor which reflects the probability In grain size, we would not expect to of intercepting a grain across its largest develop a simple relationship between chord in the direction of measurement. fracture and grain diameter. At present, No exact correction factor is known for our best means of studying this relation irregular grains. Since this error equally ship is achieved by keeping the grain size affects ail sizes, the method is still use range as narrow as possible. -45- Appendii C: Evaluation of Fractured Surfaces with Electron Microscopic Techniques The features revealed by examining fracture between fine grains also Indicates balllstically fractured surfaces with the low resistance to the propagation of frac electron microscope arc useful in deter ture. Slight adjustments in the fracture mining modes of fracture. The two major front must occur to maintain intergranular features of interest in this investigation fracture. If a grain in the path of the were 1) the amount and orientation of fracture exceeds a certain critical size, 9 10 hackle marks (river line patterns), ' the portion of the fracture front that en and 2) the general roughness of the surface counters this grain may be converted to in relation to the grain size. Hackle an alternative mode of fracture (trans marks in fractured surfaces provide in granular. crack branching, etc.) to formation about 1) the amount of trans- sustain the fracture front. This conver granular fracture, 2) the direction of sion or initiation of new fracture con fracture, and 3) the relative amount of sumes energy. energy required to propagate the fracture. The balllstlcally fractured surfaces of Hackle marks only appear across trans- the targets were evaluated with the aid granularly fractured grains. The fracture of the electron microscope techniques. velocity it, decreased as a result of the Ballistically fractured surfaces near the Increased surface energy generated during point of impact were recovered for these the formation of hackle.9,10 Hackle evaluations. Misleading conclusions marks indicate the direction of fracture, could be drawn from comparing fractures since they are parallel to the direction of formed by different Impact velocities. fracture. To avoid this problem, the fractured sur The roughness of the fractured sur faces of each material were examined over face Is also related to energy required to a range of ballistlcally impacted velocities. propagate the fracture. Smooth fractured The fractured surfaces were examined surfaces across large grains (transgranular directly on the scanning electron micro fracture) with little or no hackle Indicate scope of magnifications of £10,000X. relatively low resistance to the initiation Replicas of the fractured surfaces were and propagation of the fracture. The examined with other electron microscopes fine or shallow roughness of intergranular to magnifications of £10O,O00X. -46- Appendix D: The Collection and Characterization of Powders Generated by Ballistic Impact The methods used to collect and evalu target debris. Wax-coated aluminum ate the debris from balllstically impacted plates were positioned to face the ceramic targets of Be.B and BegB bonded to plates for collection of the debris In front 6061-T6 aluminum backup plates are de of the targets, and wax-coated cardboard scribed below. The reasons for develop plates were positioned In back of the alu ing these methods are discussed in the minum backup plates to collect the debris section on beryllium boride toxicity. from the targets that were penetrated Two ecfttecttam tytAtma were Incorpo (s*e Fig. O-W. ?«tte\M greator than rated into our existing ballistic test facil -5000 n in diameter are not considered as ities to collect batUstically generated debris for these studies. Composite armor - Ceramic / /- Epoxy bond Aluminum backup plato (6X6X1/4 In.) Projectile path -»" Acoustic tile to trap projectile - Aluminum plate coated Cardboard plate (6 in. diam) with 1/4 in. of wax coated with 1/8 in. of wax (Carbowax 750+1000, 1:3) (Carbowax 750+1000, 1:3) Fig. D-1. Schematic diagram of the two collection systems used to collect the bal- listically generated debris in front and in back of composite armor targets. -47- When the projectile penetrated the centrating the debris in the bottom of a target the debris that was carried through test tube with a centrifuge, 3) decanting the hole in the backup plate was collected the solution, and 4) repeating (-6 times) in the wax-coated cardboard plate. Thin the above steps until the wax was cardboard plates were used in this position removed. Ar intermediate step to dis since the thin cardboard did not signif solve projectile debris was included in icantly reduce the velocity of the projec this operation by using dilute acid solution tile, and the velocity of the debris was gen instead of water during the third rinse. erally low enough so that the cardboard After the final decanting the debris wa? was not penetrated by the debris. Since vacuum dried and weighed. The debris the velocity of the projectile was not signif was screened through sieves to determine icantly reduced by the cardboard, the the upper portion f>45 n diam) of the size existing methods of estimating the velocity distribution curve. The finer debris of the projectiles that penetrate the target (<45 ii diam) was weighed before deter wore not altered. The small amount of mining its size distribution curv by a debris carried along with the projectile was centrifugal sedimentation technique (MSA lost. The debris imbedded in the wax was partlcle-slze analyzer from the Mine removed for particle size determinations. Safety Appliances Company). Examples The debris was removed from the wax of these results are plotted In by 1) dissolving the wax In water, 2) con Figs. 36-41. -48. References M. L. Wilkins, C. A. Monodel, and D. R. Sawle, An Approach to the Study of Light Armor. Lawrence Livermore Laboratory, Rept. UCRL-50284 (1967). M. L. Wilkins, Third Progress Report on Light Armor. Lawrence Livermore Laboratory, Rept. UCRL-50460 U968>. M. L. Wilkins, C. F. Cline, and C. A. Honodel, Fourth Progress Report on Light Armor Program, Lawrence Livermore Laboratory, Rept. UCRL-50694 (1969). II. L. Wilkins, C. F. Cllne, and C. A. Honodel, Light Armor. Lawrence Liver more Laboratory, Rept. UCRL-71817 (1969). M. L. Wilkins, R. L. Landingham, and C. A. Honodel, Fifth Progress Report of Light Armor Program, Lawrence Livermore Laboratory, Rept. UCRL-50980 (19V1) (OUO). A. E. Abey, J. Appl. Phys. 4±, 5254-5259 (1970). G. L. Kehl, The Principles of Metallographic Laboratory Practice (McGraw-Hill Book Co., New York, 1949), 3rd ed. V. D. Frechette, Alfred University, private communication (1970). H. Liebowitz, Ed., Fracture, Vol. II (Academic Press, New York and London, 1968). B. L. Averback, D. K. Felbeck, G. T. Hahn, and D. A. Thomas, Eds., "Fracture," in Proceedings of an International Conference on the Atomic Mecha nisms of Fracture (Swampscott, Massachusetts, April 12-16, 1959). F. L. Harding and D. R. Rossington, Journal of the American Ceramic Society 53, 87 (1970). S. K. Rhee, Journal of the American Ceramic Society 54. 332 (1971), H. K. Stokinger, Beryllium. Its Industrial Hygiene Aspects (Academic Press, Ne>. York and London, 1966). G. D. Darwin and J. H. Buddery, Beryllium (Academic Press, London and New York, 1960). H. E. Giffin, Evaluation of Beryllium-Oxide, Office of the Surgeon General, OTSG No. 192806, MEDPS-PO, February 10, 1967. M. L. Torti and J. W. Herrick, "Effectiveness of Various Spall Shield Configura tions," in Proc. 73rd Annual Meeting of the American Ceramic Society (Chicago, Illinois, April 24-29, 1971). H. E. Stokinger and L. D. Scheel, Laboratory of Toxicology and Pathology, Bureau of Occupational Safety and Health, Department of Health, Education and Welfare, Cincinnati, Ohio, private communication (1971). D. A. Everest, The Chemistry of Beryllium (Elsevier Publishing Company, Amsterdam, London and New York, 1964). W. Slavin, Atomic Absorption Spectrography (Interscience Publishers, New York, 1969), pp. 84-85. -49- r :. ••<• • "'••»•• L. P. Rlgdon and M. C. Waggoner. Determination of Boron In Boratea. Boron Hydrides. Organo-Boron Compounds. Elemental Boron and Refractory Borldes. Lawrence Llvermore Laboratory, Rept. UCRL-S0948 (1970). J. W. Fischer, C. J. Morris, J. W. Frazer, and E. R. Fisher, "Automated Vacuum Fusion Apparatus," In 1970 Analytical Chemistry Annual Report, Lawrence Livermore Laboratory, Rept. UCRL-50006-71 (1971). pp. 16-17. 50' ; NOTICE "llii npatl «M pnptrad •» u MCMUI of work spomond by Itu IMM Sutw GonrMHnl^ Nfthtr UK Urttd SWIM nor Ibt IMM Stem Atomic Eaarcy CommWoa, nor »y of tMr MiployMi, m »y of IMr contricMi, lutxofilracton, or Heir tmflartm. Mt« »ny wimMyi una or InobKl. or >"U«KI uiy lipl ItaWrty or r«p«a(Hity for On iccimcy. compMono* or iMeAibmi of any infonnitloB.appftrilia, product or proem illorloiu, or i«pn—a Hut H» at wauld not Mrlon pHil«ly- Printed in USA. Available from the National Technical Information Center, National Bureau of Standards, U.S. Department of Commerce, Springfield, Virginia 22151 Price: Printed Copy $3.00; Microfiche $0.95.