ABSTRACT AN ABSTRACT OF THE THESIS OF GEORGE J. DOOLEY III for the Doctor of Philosophy in Materials Science presented on May 7, 1969. Title: Effects of Selected Minor Alloying Additions on the Structure and Deformation Characteristics of Beryllium Abstract approved: William D. McMullen Solid solution alloying was employed in an attempt to produce some relatively ductile form of beryllium. If the c/a ratio could be significantly altered, it was felt new or different slip systems could be activated. The following elements were selected on the basis of atomic size, melting point, crystal structure and density for adding to beryllium in amounts of 0. 5, 1.0, 2.0, 3.0, 4.0, 5.0 and 10.0 atomic percentages: boron, manganese and, titanium. All samples were non -consumable arc melted, machined and sectioned for wet chemical, spectrographic, X -ray diffraction and metal - lographic analysis as well as for mechanical (compression) testing. These tests showed all alloy samples exceeded the solubility limits in each respective system. Be4_5B, Be8Mn and Be12Ti'were identified as the second phases in the individual systems. Beryllium -boron alloys ex- hibited an eutectic or peritectic reaction and the eutectic composition in the beryllium -manganese system was established at 22.0 weight percent manganese. The samples Be /0. 5B, Be /1.0Mn and Be /0. 5Ti gave yield strengths of 47, 200 psi, 56, 600 psi and 81, 250 psi respectively in compression testing. These same specimens yielded work hardening rates of 1.07 x 106 psi, 1.3 x 106 psi and 1. 52 x 106 psi respectively. Long wide twins in pure beryllium were accompanied by large amounts of cross -slip. The boron sample displayed long wide twins and also very short narrow twins, no cross -slip and extensive areas with microcracks present. Shorter and narrower twins characterize the manganese specimens. The beryllium- titanium alloys exhibited extremely small twins emanating from particles of second phase Be12Ti; however, the majority of the twins in this system are long, extremely narrow and are seen to be internally con- stricted along the length of the twin. Thése constrictions have been ascribed to a strain relief process which further prevented the twin from growing parallel to its shorter dimension. The near total absence of cross -slip in the three alloy systems was attributed to a lessening of the stacking fault energy as a result of in- creasing the solute concentration. The drop in the stacking fault energy decreases the probability for cross -slip, makes extensive deformation difficult and explains higher yield strengths and work hardening rates. Evidence presented suggests slip occurs prior to gross twin propagation. The relationship betw twinning shear and twin shape suggests for the beryllium- titanium alloys twinning on higher order planes (e. g. , {.1121} or 11122 }) rather than the {1012} twinning normally observed. Effects of Selected Minor Alloying Additions on the Structure and Deformation Characteristics of Beryllium by George Joseph Dooley III A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy June 1969 APPROVAL SHEET APPROVED: Associate Professor of Mechanical Engineering Head of Department of i chanical Engineering Dean of Graduate School Date thesis is presented May 7, 1969 Typed by Joyce McInnis for George J. Dooley III ACKNOWLEDGMENTS The author would like to express his gratitude to the U.S. Bureau of Mines, Albany, Oregon and to Oregon State University, Corvallis, Oregon, whose cooperative agreement made this research work possible. Although many Bureau of Mines' personnel were helpful throughout the course of this work, particular thanks must be extended to members of the Metals Pro- cessing branch under the direction of Mr. : obert Beall, to members of the Materials Science branch under the direction of Mr. Hal Kelly and to Mr. Jim Wilderman of the drafting section for his work on the figures and draw- ings. Mrs. Joyce McInnis, typist and secretary, deserves more praise than thanks for her efficiency, assistance and good nature during the author's stay at the Bureau of Mines. The majority of the technical guidance for this piece of research was provided by Dr. William McMullen of Oregon State University. His unique personality 'coupled with technical competence provided the latitude necessary for carrying through a research project of this type. His suggestions and guidance gave more directionality to the work and saved many hours time when the author's efforts would perhaps have proceeded along other avenues of approach. The author's sincere appreciation is extended to him for his aid and cooperation. The greatest debt of any must be paid to the author's wife for her patience, hard work and encouragement throughout this somewhat trying academic period of life. Her willingness (and often insistence) , ;. tine and and research efforts on the part of the author before their personal while family obligations was indicative of the continuing support received have been working as a graduate student. Without her aid the work would less enjoyable, less meaningful and certainly much less rewarding. TABLE OF CONTENTS Page INTRODUCTION 1 THEORETICAL BACKGROUND 8 REVIEW OF LITERATURE 30 MATERIALS 97 APPARATUS AND EXPERIMENTAL PROCEDURES 102 Weighing and Compacting 102 Nonconsumable Arc Melting 103 Machining and Sectioning 108 Metallographic Analyses 109 X -ray Diffraction Analysis 110 Chemical and Spectrographic Analyses 112 Compression Testing 113 EXPERIMENTAL RESULTS 116 X-ray Diffraction 116 Metallography 118 Mechanical Deformation 124 Slip and Twinning 128 DISCUSSION AND CONCLUSIONS 151 SUMMARY 169 TABLE OF CONTENTS (Continued) Page SUGGESTIONS FOR FUTURE WORK 172 BIBLIOGRAPHY 175 LIST OF FIGURES Figure Page 1 Planes in an hexagonal lattice with a common [1210j direction 9 2 Important planes and directions in an hexagonal close packed metal 11 3 Crystallographic directions and planes in hexagonal close packed beryllium 12 4 Slips, fracture and twin planes in beryllium 14 5 Effect of temperature on the critical stress for (0001) slip and (1010) slip 15 6 The compounds of beryllium 83 7 Nonconsumable arc melting button furnace 104 8 Second phase Be4_5B in beryllium -boron alloys 120 9 Eutectic phase in Be /4. 0VM 122 10 Be8Mn phase in Be/ 1. 0Mn 125 11 Be12Ti phase in Be/ 0. 5Ti 126 12 -A Microstructure of deformed pure beryllium 130 12 -B 12 -C Typical deformation twins in pure beryllium 131 13 Straight slip lines in pure beryllium 132 14 Crow: slip in pure beryllium 133 15 Slip lines crossing twins in pure beryllium 134 LIST OF FIGURES (Continued) Figure Page, 16 Typical deformation twins in Be/ 0.5B 136 17 Microcracks in Be/0. 5B 138 18 Curved twins in Be/0. 5B 139 19 Representative deformation twins in Be/1. OMn 140 20 Very narrow twins in Be/1. OMn 141 21 Twin intersections in Be/1. 01\Tri 143 22 Extensive twinning in Be/1. Clitin 144 23 Short twins and second phase in Be/ O. 5Ti 145 24 Narrow twins in Be/0. 5Ti 146 25 Slip lines in Be/0. 5Ti 14 8 26 Irregular twins in Be/ O. 5Ti - 149 27 Slip crossing twins in Be/0. 5Ti 150 LIST OF TABLES Table Page I Modes of slip in hexagonal metals 22 II Beryllium deformation behavior 40 III Microstructure of binary beryllium alloys as melted 74 IV Beryllium starting material analysis 100 V Alloying element analysis 101 VI Alloy compositions after arc -melting of samples used in compression testing experiments 124 VII Work hardening rates and yield strengths for beryllium alloys 127 EFFECTS OF SELECTED MINOR ALLOYING ADDITIONS ON THE STRUCTURE AND DEFORMATION CHARACTERISTICS OF BERYLLIUM INTRODUCTION The potential of the metal, beryllium, has been recognized for some time. Its notable characteristics are low density, high elastic modulus and its high strength -to- weight ratio (61). Its density (1. 848 grams per cubic centimeter) approaches that of magnesium, yet beryllium melts some 600° C higher than magnesium. Its elastic modulus is approximately 140 percent that of iron, however, it is less than one -fourth as heavy. Its electrical conductivity is approximately 40 percent that of pure copper (2). But, use of pure beryllium in industrial applications has never signifi- cantly materialized. Beryllium has not realized its full potential in indus- trial applications because of its lack of so- called third -dimensional ductil- ity. The term "third- dimensional ductility" infers that plates and sheets of beryllium can be successfully fabricated, but these structures are in- capable of supporting any bending or any significant forces perpendicular to their major plane of symmetry. Efforts to fabricate beryllium by con- ventional means of fusion, casting and extrusion, have been only partially successful. It is possible to limitedly manipulate the ductility of beryllium, but each particular application requires a careful study of the fabrication methods so as to produce optimum ductility in a specific direction by a 2 compromise of the ductilities in the other directions. This fact is physical evidence for the known anisotropy of beryllium. Beryllium has other features not related to the ductility aspect which make it a valuable material. These will not be of interest in this work; however, they should be mentioned for the sake of completeness. Beryllium is characterized by some outstanding nuclear properties. It has an extremely low neutron capture cross section and a high neutron scattering cross section which make it useful as a moderator and reflector for thermal nuclear -power reactors. During the last few years emphasis in the application of beryllium has shifted from nuclear applications to so- called "space applications" and the latest development of beryllium has been in connection with the various rocket, missile, and aircraft projects. Nevertheless, two main factors have delayed a wider application of beryllium in industry.