Hydrogen Embrittlement of Tough Pitch Copper by Brazing

Testing the effects of six variables statistically shows factors that can cause, enhance, or have no effect on embrittlement

BY E. BELKIN AND P. K. NAGATA

ABSTRACT. Hydrogen embrittlement cuprous oxide particles. some were not. of ETP (Electrolytic Tough Pitch) Above 374 C the critical temper­ Two time periods at temperature copper due to brazing has been ature of water, steam is the only form were used to evaluate the effect of studied. The authors have found that in which water exists, and the pres­ time. Ten cylinders comprised a run. the major causative factor of hy­ sures generated can reach as high Five replications were made of each drogen embrittlement when using as 80,000 psi (5.52 X 102 MPa). The run and they were made consecu­ fluxed brazing alloys was the water of phenomenon usually manifests itself tively. hydration in one of the flux constitu­ as large fissures and cracks (see The experimental cylinders are ents. Time at brazing temperature Fig. 1), although only oxide deple­ shown in Fig. 3. Each of the four holes was found to strongly influence the tion may be observed (Fig. 2). in the cylinder was stopped by a con­ depth of embrittlement, a longer time Hydrogen embrittlement does not ical shaped piece of ETP copper leading to a greater depth of em­ seriously affect the tensile strength or (Fig. 4). These cones were lightly brittlement. Different brazing filler elongation of ETP copper, but does held in place so that the gas pressure metals give varying depth of em­ affect its fatigue strength (Refs. 5,6). in the holes would need to be a little brittlement. Bright dipping the copper Therefore, it must be avoided in any greater than atmospheric pressure in and manually handling the brazing structure that may be subject to order to escape. This was done in an alloys do not significantly increase or cyclical stress or vibration. effort to confine the gas products to decrease the amount of em­ In general, hydrogen embrittle­ some degree but not confine them so brittlement. ment of brazed copper was thought to as to cause a steam explosion. occur only during furnace brazing Three brazing filler metals were Introduction where the furnace gas was too reduc­ used. Their compositional limits are ing for that temperature (Refs. 7,8). in Table 1. The hydrogen embrittlement of However, this study has shown that The flux is a general purpose braz­ ETP (Electrolytic Tough Pitch) cop­ embrittlement can occur in circum­ ing flux. Its composition was deter­ per is a well known phenomenon stances other than by heating in mined by the Westinghouse R&D (Refs. 1,2). Hydrogen diffuses into reducing furnace gases. laboratory and the results are shown the copper as atomic hydrogen and in Table 2. Prior to the test the flux reacts with the cuprous oxide par­ Experimental Procedure was stirred so that a homogeneous ticles to produce copper and water. mixture was achieved. This can occur at temperatures as low The experiments were run with ETP The cylinders were bright dipped as 150 C but is usually encountered copper cylinders each having four for three minutes to remove any oils at higher temperatures (above 400 C) holes to allow evaluation of four vari­ or surface oxides. The bright dip anal­ (Ref. 3). ables under common conditions. The ysis is shown in Table 3. Below 374 C the phenomenon three brazing filler metals tested con­ A test run consisted of 10 cylinders. generally manifests itself as an oxide sisted of two alloys that require flux Since the bright dipping operation depletion or as holes at the sites of under normal brazing conditions in air leaves some hydrogen adsorbed in and a so-called fluxless alloy. The two the surface of the copper, some of the brazing filler metals that require flux specimens were subjected to a E. BELKIN and P. K. NAGATA are with the were tested with and without flux. vacuum of 10_e torr and held for 24 Materials and Process Engineering group, The tests with flux were evaluated with hours at 200-300 F (93-144 C). This Large Rotating Apparatus Division, wet and dried flux. procedure will rid the copper of much Westinghouse Electric Corporation, East Pittsburgh, Pa. 15112. All the cylinders were bright of the adsorbed hydrogen (Ref. 10). It Paper was selected as alternate tor the dipped. Some were vacuum treated preceded the experiment by no more 55th AWS Annual Meeting held at Hous­ prior to testing to remove hydrogen than 36 hours. ton, Texas, during May 6-10, 1974. adsorbed during bright dipping and The variables tested are listed

54-s | FEBRUARY 1975 Fig. 1 — Hydrogen embrittlement. Brazing filler metal B wet flux, 4 min at brazing temperature, x200, reduced 28% Fig. 2 — Oxide depletion. Brazing filler metal C, 1 min at brazing temperature, x200, reduced 28% below: .19 Diameter x 1.25 Deep 1. One minute vs four minutes at 4 Ho Ies Equal Iy Spaced brazing temperature. As Shown On .5 Diameter 2. Flux with physical water and water 125— — of hydration vs flux with water of Bo 11 Circle. hydration only. Chord = .354- 3. Bright dipped vs bright dipped and vacuum treated. Vacuum treat­ ment removes the effect of bright dipping. 4. Body oils vs no body oils. Fig. 4 — Stoppers for cylinder holes 5 Wet flux vs no flux. 6. Brazing filler metal A vs brazing filler metal B. above are used to analyze data, to The five test runs were made in the find the standard deviation, and to following manner: test hypothesis regarding the vari­ 1. The flux was stirred to achieve ables in an experiment. homogeneity. The effects that were studied were 2. Eight parcels of wet flux, 0.20 time at brazing temperature, wet vs grams each, were weighed out and dry flux, vacuum treatment vs no placed in the appropriate holes. vacuum treatment after bright dip­ 3. Four 1 X 1/16 in. (2.54 cm X 0.16 ping, presence of body oils, presence cm) diam pieces of each brazing of flux, and brazing filler metal A vs filler metal were placed in their brazing filler metal B. The six vari­ proper places. The pieces of braz­ ables are examined in Tables A4, A5, ing filler metal were degreased A6 and A7 in Appendix I. Their iden­ and not manually handled except tification numbers with "—" and "+" where noted in Table 4. level assignments are given in Table 4. The copper cones were placed in 5. The results are shown in Table 6. the holes. Significance occurs when the F- 5. The samples were induction braz­ value of a variable (last column on ed at 10 kHz using the procedure right in Tables A4-A7 in Appendix I) below: exceeds the 95 percent point of F1i64 a. Heating time from room (Fi,32 in Table A7) (bottom line in temperature to 1400 F(760 C): tables). This means that the prob­ 1 minutes ability that the variable has no effect b. Time at temperature: 1 or 4 on the depth of embrittlement is less minutes than five percent. c. Air cool This probability could be de­ 6. The samples were then cut in half Fig. 3 — Experimental cylinders creased by using a one percent along their axial length and metal­ significance level, but this would in­ lographically sectioned. Prohas- crease the probability of missing real ka's etchant was used to etch the effects. samples. Its constituents are H20 eral, oxide depletion did not exceed Figure 5 (see Appendix 1) is a sug­ (distilled). 70 ml; HCI (reagent 0.5 mils or 0.0005 in. (0.0127 mm) so gested "four dimensional plot" of the strength), 25 ml; Fe (N03)3, 5 gm. that its contribution to the total 16 average embrittlement values The experimental results are pre­ measurement is negligible. The data found in Table A4 of Appendix 1. sented in Table 4. The data are mea­ are analyzed in Appendix I using Since four dimensions cannot be surements of the depth of embrittle­ Yates' Algorithm, ANOVA (Analysis of presented, a cube having two data ment and/or oxide depletion. In gen- Variance) tables, and the F-test. The points at each corner is used.

WELDING RESEARCH SUPPLEMENT! 55-s Table 1 — Brazing Filler Metals and Composition (wt %) Brazing filler metal Ag Cu Zn P Cd Impurities Equivalent specifications

QQ-B-655, Class FS BAg-6 A 49-51 33-35 14-18 — 0.15 Max AWS 5.8-69 BAg-6

QQ-B-655. Class FS BAg-la MIL B 15395A Gr. 4 B 49-51 14.5-16.5 14.5-18.5 — 17-19 0.15 Max. AWS 5.8-69 BAg-la

C 14.5-15.5 Remainder — 4.8-5.25 0.15 Max MIL-S-15395, Gr. Ill QQ-S-561, Class III A AWS 5.8-69 BCuP-5 QQ-B-655, Class FS BCuP-5

spread. However, this practice causes (a) Table 3 — Composition of Bright Dip Table 2 — Composition of the Flux hydrogen evolution at the surface of the copper and may cause some ad­ sorption of hydrogen into the copper Item Dilution Weight % Constituents Weight % matrix. Upon heating with or without brazing alloy and flux, this adsorbed H S0 96% H SO„ 61 hydrogen causes some embrittle­ KBF, 25 2 4 2 + 4% H20 ment in the former case and in­ K2B40, 35 HN03 70% HNO3 30.5 creased embrittlement in the latter. K2B407(5H20) 9 + 30% H20 H20 31 The effect of adsorbed hydrogen is HCI 37.5% HCI 1.0 shown in Tables A1 and A5 in Appen­ + 62.5% H20 H 0 7.5 dix I. It is variable 3. As can be seen, (a) Composition was determined by laboratory analysis 2 — vacuum treatment after bright dipping decreases embrittlement in the case of brazing filler metals A and B. This The notation for corners I and II of Results effect, however, is significant in only Fig. 5 are explained below: one case, namely, Table A4. I. 1,W ,NV =1 minute at brazing Brazing Filler Metals A & B temperature, wet flux, Presence of Body Oils (B) no vacuum treatment vs No Body Oils (-) B:4.3 Brazing filler metal B: These brazing filler metals normal­ average depth of em­ ly require flux. Table 4 of the text and Manually handling brazing filler brittlement 4.3 mils Tables A4, A5 and A6 of Appendix I metals can lead to surface con­ A:4 .6 = Brazing filler metal A: show the results for the above filler tamination of the brazing filler metals average depth of em­ metals with wet and dry flux, and no with body oils or sebum. This could brittlement 4.6 mils flux and wet flux. lead to increased embrittlement if the body oils decompose at high tem­ 4,D V = 4 minutes at brazing temperature, dry flux, Dry (D) vs peratures to form hydrogen and other vacuum treatment Wet (W) Flux elements. On the other hand, the B:3.0 = Brazing filler metal B: body oils could decrease the amount Tables A4 and A6 from Appendix I average depth of em­ of embrittlement by coating the braze show the differences in dry and wet brittlement 3.0 mils so that the water vapor could not flux. They appear as variable 2. A:7.2 = Brazing filler metal A: readily reach the braze thus lowering Comparing the 95 percent point of average depth of em­ the amount of hydrogen liberated. F 4 (3.99) to the F value for variable brittlement 7.2 mils 16 The tests for this effect are seen as 2 in the two tables (0.89 in Table A4 The variable 4 in Table A6 in Appendix I. cube in Fig. 5 represents the and 0.0 in Table A6) shows that Fi,64 effects which can be shown in the The results show that for brazing filler is larger than the F values of variable metals A and B, the presence of body sketch below. 2. This means that the difference be­ oils decreases the amount of em­ tween wet vs dry flux is not significant brittlement observed, though the ef­ at the five percent level. fect is not statistically significant.

Time (1 vs. 4 minutes) Wet Flux (W) vs No Flux (N) The effect of time (variable 1) can The effect of the presence of flux be seen in Tables A4-A6 in Appendix is seen in Table A5, variable 5 in Ap­ I. In all cases the chance that the dif­ pendix I. A comparison of the F-value ference between one and four minutes at brazing temperatures is to that of F164 indicates that the ef­ fect of the presence of flux is a signif­ not real is less than five percent. This icant factor in increasing hydrogen would indicate that the differences embrittlement. observed are significant. The arrows point in the positive A time effect would be expected directions of the Yates Algorithm in because a longer time at temper­ Vacuum Treated (V) vs Appendix I. Using a + to indicate an ature would allow the hydrogen to dif­ Not Vacuum Treated (NV) effect in the positive direction and a - fuse farther down the grain boun­ for the negative direction, corners I The practice of bright dipping daries and cause further embrittle­ and II can be represented by Table 7. copper before brazing is very wide­ ment.

56-s | FEBRUARY 1975 Table 4 — Experimental Set-Up and Results

Embrittlement depth in mils for replicate numbers Used in Table 0) Avg, Avg, 2 4 5 t? ^° K

V-1 A 1 N A X 3.2 0.6 0.0 0.0 1.2 1.0 0.025 B 1 N B X 0.0 0.5 0.0 0.8 0.0 0.3 0.008 C 1 N C 0.0 1.3 1.5 1.8 0.0 0.9 0.023 D 1 N C 0.6 0.6 0.6 0.8 00 0.5 0.013

V-2 A 4 N A 1.0 1.5 1.5 0.6 1.4 1.2 0.030 B 4 N B 0.0 0.8 0.0 1.0 0.0 0.4 0.010 C 4 N C X 0.6 0.0 0.6 1.0 1.5 0.7 0.018 D 4 N C X 2.5 0.8 2.5 0.8 3.5 2.0 0.050

V-3 A 1 D A X X 5.0 7.8 3.5 3.2 5.7 5.0 0.127 B 1 W A X X 4.7 4.1 3.8 4.7 8.1 5.1 0.130 C 1 D B X X 1.0 1.3 0.8 1.4 2.0 1.3 0.033 D 1 W B X X 2.4 0.8 0.0 0.9 4.4 1.7 0.043 V-4 A 4 D A X X 6.3 7.0 6.9 8.0 7.6 7.2 0.183 B 4 W A X X 1.3 5.7 8.1 12.6 5.7 6.7 0.170 C 4 D B X X 1.9 1.9 3.8 1,3 6.3 3.0 0.076 D 4 W B X X 0.6 1.5 2.3 4.9 5.7 3.0 0.076

V-5 A 1 D B A X 4.4 3.8 4.1 4.1 6.3 4.5 0.114 B 1 W B A X 2.7 3.2 3.7 5.2 5.0 4.0 0.102 C 1 D B B X 0.8 0.6 0.9 2.0 4.4 1.7 0.043 D 1 W B B X 0.0 0.8 4.1 1.8 5.7 2.5 0.063

V-6 A 4 D B A X 5.0 4.4 5.1 6.2 6.0 5.3 0.135 B 4 W B A X 4.4 6.3 5.4 3.5 8.5 5.6 0.142 C 4 D B B X 0.0 1.9 1.9 3.6 5.7 2.6 0.066 0 4 W B B X 0.0 2.3 2.5 3.6 2.0 2.1 0.053

(a) N = no flux; D = dry flux; W - wet flux. (b) - = no body oils; B = presence of body oils.

Brazing Filler Metal A vs Table 5 — Identification of the Variables Tested Brazing Filler Metal B (A vs B) Variable tested in Appendix Table No. The effect of using brazing filler metal A instead of brazing filler metal Levels B is variable 6 in Table A4-A6 of Variable A1 A2 A3 A4 Appendix I. In all cases the embrittle­ — + ment from brazing filler metal B was less than that for brazing filler metal Time (minutes) 1 4 X X X X A. The chance that the above men­ Wet or dry flux Dry Wet X X tioned differences are real were all (D) (w) more than 95 per cent. Vacuum treatment No after bright Vacuum Vacuum Brazing Filler Metal C dipping (NV) (V) Presence of body - B X X As previously mentioned, brazing oils filler metal C did not require any flux Presence of flux Wet None X when used with copper having no (W) (N) grease or flaky oxides on the surface. Brazing filler A B X X X The only effects studied were time, metal

WELDING RESEARCH SUPPLEMENTl 57-s the presence of body oils, and the count for all the embrittlement tor in only one of the two cases tested. presence of adsorbed hydrogen. observed. In neither case were the results Time increases the embrittlement. statistically significant. In any case, The statistical analysis in Appendix I Brazing Alloy the presence or absence of body oils shows that time is the only statistical­ cannot explain the amount of em­ ly significant variable. Differences in Analyses for hydrogen were made brittlement observed. the amount of embrittlement ob­ on the brazing filler metals and they served exist for the other two vari­ show that the filler metals contain Flux ables but they are not statistically about 0.2 ppm by weight hydrogen The results from NV, N (no vacuum significant. (Ref. 11). A brazing filler metal containing 0.2 treatment, no flux) vs NV, W (no ppm hydrogen would cause em­ vacuum treatment, wet flux) show that Discussion brittlement in an ETP copper having the presence of flux with the brazing The foregoing results show that 0.04 weight per cent oxygen as oxides filler metal is definitely a statistically hydrogen embrittlement does occur to a maximum depth of about 0.086 significant factor in the hydrogen em­ during brazing. It seems, however, mils (33.8 microns) (see Appendix III) brittlement of ETP at brazing temper­ that brazing filler metals that use flux if ail the hydrogen diffuses into the atures. suffer more embrittlement than the copper. The results from the W (wet flux) vs one that did not. This is far too small an amount D (dry flux) for brazing filler metals A In the above tests there are only a needed to cause hydrogen em­ and B show that while wet flux may brittlement of the magnitude that is have some beneficial effect upon the few sources from which H2 and/or seen for the most severe cases, e.g., depth of hydrogen embrittlement, the H20 can come. They are the air in the laboratory, the bright dipping, the 5-6 mils. effect is not statistically significant. It brazing filler metal itself, the body oils is therefore not this physical water from the experimenter's fingers, and Body Oils that causes the major portion of the the brazing flux. These will be dis­ deep hydrogen embrittlement. cussed in turn below. The results from B (body oils) vs The only other source of hydrogen (-) no body oils show that the pres­ in the flux is the water of hydration in Laboratory Air ence of body oils is a beneficial fac­ the potassium tetraborate (K2B407-

The conditions under which the tests were done were not very un­ usual. Great extremes in temper­ Table 6 — Variables Producing Lower Embrittlement ature and humidity were not ex­ perienced in the laboratory. Further Lower embrittlement variables, the tests were conducted during the Variable Levels as treated in Appendix Tables winter months. The air outside the laboratory would have had to be A1 A2 A3 A4 heated before it entered the room. Heating air tends to lower its relative •|(a) humidity. Time (minutes) 1 4 ,(•) 1•w lb) 1« If the humidity were relatively con­ Wet or dry Dry, Wet, Wet nd stant, its effect would be equal for all flux (D) (W) Vacuum treated No the tests. Therefore the air in the a after bright vacuum, Vacuum r< > NV laboratory is assumed to have a dipping (NV) (V) negligible effect on the tests. Presence of None Yes, body oils (-) (B) Presence of Wet, None, Bright Dipping flux (W) (N) Filler metal A B ,(a) ,ia) .(a) The results from NV (no vacuum treatment) vs V (vacuum treatment) (a) Statistically significant at the 5% level show in only one of three cases a (b) No difference statistically significant difference in embrittlement between the two treatments. Table 7 - The foregoing results seem to be - C orners I and I I as Shown in Fig. 5 inconclusive because one would ex­ pect that the presence of adsorbed Corner I hydrogen would have the same effect on the depth of embrittlement regard­ less of the type of brazing filler metal Flux Filler metal used in the test. That the vacuum Time state Treatment Composition treatment after bright dipping de­ creases embrittlement in both test B:4.3 - + _ + cases involving brazing filler metals A A:4.6 - + and B but not for brazing filler metal C may suggest that a hitherto unfore­ Corner II seen phenomenon is occurring. More tests are needed on this point. Flux Filler metal The inconclusiveness of the data Time state Treatment Composition indicate that bright dipping may intro­ duce sufficient hydrogen into the B:3.0 - + + + copper matrix to affect the depth of A:7.2 - + — + — embrittlement but not enough to ac­

58-s I FEBRUARY 1 975 Acknowledgments 5H20). embrittlement according to the The H20 must have some element equation. The authors would like to express their which reduces it according to the appreciation to A. R. Pebler and M. Stratis Cu 0 + 2H -» 2Cu + H 0 equation below: 2 2 for the meticulous care with which they The values of the Gibbs Free conducted the experimenta. Thanks are xMt H20 -+ MxO + H2 Energy for the combined equations also due R. M. Slepian and J. P. Prohaska The elements that are as active or are negative (see Appendix II). This for their excellent metallography without which this paper would not have been nobler (less active) than copper can­ indicates that the overall reaction is at written. not cause the above reduction of H20. least possible. What may occur de­ Special thanks are due L. D. Kunsman Also, the reduced activity of copper in pends upon the reaction kinetics. for his discussion in initiating this project, the brazing filler metal would reduce The kinetics of the reaction may ex­ and to Dr. K. L. Kussmaul of the Mathe­ the amount of hydrogen gas pro­ plain why brazing filler metal B seems matics Department for his help in this work duced. to give less enbrittlement than braz­ (specifically of his contribution to the sec­ Therefore, one must look for a ing filler metal A. Cadmium tarnishes tion on the statistical analysis and dis­ metal that is more active than copper. in air (Ref. 13). The resulting oxide cussion). In the case of brazing filler metal A may shield the surface of the brazing this element is zinc and in the case of filler metal so that the water of hydra­ brazing filler metal B it is zinc and tion will not be able to react with the References cadmium. zinc and cadmium to form hydrogen. The proposed sequence of steps in 1. Harper, S., et al, Journal of the the reaction is: Institute of Metals, 1961-1962, Vol. 90, p. Conclusions 414. a. The active metal reacts with the 1. Hydrogen embrittlement occurs to 2. Finlay, W. L., Silver-Bearing Copper, Corinthian Editions, New York, 1968, p. H20 that comes from the water of some extent with all three brazing 111. hydration. This reaction produces filler metals investigated. 3. Harper, S., et al, Ibid, p. 414. the oxide of the active metal and 2. Hydrogen embrittlement is par­ 4. Finlay, W. L., Ibid, p. 111. hydrogen, as shown above. ticularly enhanced by the use of 5. Harper, S., et al, Ibid, p. 416. b. The hydrogen gas then enters the fluxes. It is not the water that is 6. Morin, D. L., unpublished data. copper as atomic hydrogen. used as a binder (physical water) 7. AWS Brazing Manual, American that causes the embrittlement but Welding Society, Miami, Fla., 1962, p. 17. H 2H 2 it is the water of hydration in one of 8. Pvt. Communication, Olivera, T. J., Staff Engineer, American Welding Society. c. The hydrogen diffuses along the the constituents of the flux. 9. Silva, H., unpublished data. 3. Bright dipping does not signif­ grain boundaries* and causes the 10. Pvt. Communication, Dr. W. T. Lind­ icantly increase the amount of em­ say, Jr., Westinghouse R&D. brittlement observed. 11. Pvt. Communication, Dr. F. P. Byrne, "Previous experiments have shown that 4. The depth of embrittlement is Westinghouse R&D. most of the embrittlement occurs along the strongly dependent on time at 12. Smithells, C. J., ed., Metals Ref­ copper grain boundaries and that the brazing temperatures, longer erence Book, Vol. 2, 3rd Edition, Butter- Cu20 particles in the copper matrix are not times giving more embrittlement. worths, London, 1962, p. 580. affected. It is reasonable to assume that 5. Manually handling the brazing 13. Hodgman, C. D., ed., Handbook of the hydrogen diffuses at least as far as the alloys does not seem to affect the Chemistry and Physics, Chemical Rubber embrittlement is observed. Calculations Publishing Co., Cleveland, Ohio, 1962, p. based on the above have revealed that at depth of embrittlement to any 409. brazing temperatures the diffusion rates significant degree. 14. Hunter, J. S., Op. Cit., vol. 4, p. 60. along the grain boundaries are 50 to 100 6. More hydrogen embrittlement oc­ 15. Private Communication, Dr. K. L. times that usually given in the literature curs with brazing filler metal A than Kussmaul, Westinghouse R&D. (Ret. 12). with brazing filler metal B. 16. Hodgman, C. D„ ed., Op. cit, p. 409.

_ „ - SUM OF SQUARE SS = The Mean Square = DEGREES OF FREEDOM DF

Applying this to the above example one sees that the Mean Squares of the The cube in Figure 5 represents a 2 Factorial test replicated five Treatments Sum of Squares are the Treatment Sum of Squares because DF=1. times. The computer printout of the analysis is presented in Table 1 of The Mean Square of the Residual Sum of Squares (the variance S ) is this appendix. The authors will present the analysis of the data in more given by 2 RSSQ familiar format, the Yates Algorithm. Sc " = -

The method used to set up the algorithm is found in many books and To test the hypothesis that the effect of a particular variable is 1U is described briefly here by quoting from Hunter: statistically significant, the F-test is used; the F-ratios in Table 1 "To transform one column of entries to the next requires tvo operations: are the ratios Variable Mean Square or MS

1. The pairs of entries, starting from the top, are algebraically s2 =rro

summed, each sum providing an entry in the next column, starting The effect of a variable is significant at the five per cent level

at the top. if its F-ratio exceeds 3.99, the tabulated 95 percent point of the F-

2. The sign of the top entry in each pair is changed, and the distribution with one and 6k degrees of freedom (DF) given at the foot

pairs are again algebraically summed, each sum providing addi­ of Table 1. Such an F-ratio would occur by chance, in the absence of a

tional entries to fill out, the bottom half of the next column." real effect, with probability less than five percent.

The procedure for performing this on the data in Figure 5 is given As can be seen, effects 1, 3, and 6 have F-ratios larger than F. ,., in Table 1 of this appendix. This means that they are statistically significant. A complete list of

Note that the numbers in the Effect Total column in Table IJ correspond the statistically significant effects in Tables U-6 is found in Table 3. to Column U of the Yates Algorithm in Table 1. In the above, the time-brazing'filler metal interaction was signif­

The analysis of variance is presented in Table 2. icant in Table 2. Caution is required, however, in declaring significance.

WELDING RESEARCH SUPPLEMENT! 59-s Table Al Table A2 Yates Algorithm for Figure 5 Estimated Analysis of Variance for Yates Algorithm in Table 1 Design Observation Column Effects

1 2 3 1. Sum of Degrees of Squares Freedom 25.1* 68.3 126.6 2U6.lt 277.7 Grand Average - 3.1-7 1631.28 80 1*2.9 58.3 119.8 131.3 7U.1 X, Effect - 1.85 963.97 1_ 22.8 6i.o 186.1 I18.8 - 19.7 X^ Effect - 0.1.9 Correction Factor 35.5 58.8 ,2 lt5.2 25.3 - 29.3 Xx Xj Effect . 0.73 tic 25.2 1*7.7 30.2 - 12.2 - U7.7 X Effect • -1.19 667.31 79 35.8 38.1. 18.6 - 7.5 - 6.5 Xx X Effect - -0.16 sy 21*.5 10.1 21.7 - 7.1. + 18.9 X2 X Effect - +0.1*7 Treatment Sum of Squares* 33.1* 23.5 15.2 - 21.9 * 19.7 X-^X Effect - +0.1*9 68.61* 1 16.1* 17.5 - 10.0 - 6.8 115.1 X,Effect - -2.88 xi 31.1 12.7 - 2.2 - It0.9 - 23.5 XjXgEffeet - -0.59 \ U.85 1 21.6 10.6 - - 11.6 *>.7 X?X,Effect +0.12 9.3 - 10.73 1 16.8 8.0 + 1.8 5.1 - H.5 XjXjX.Effect - -0.37 28.1*1* 1 6.5 1>«.9 - It.8 * 7.8 - 3>-.l X X^Effect • -0.85 X X 0.53 1 15.2 It.8 - 2.6 + 11.1 16.7 X,X,X,Effect - +0.1*2 1 3 136 1 6.5 8.7 - 19.7 • 2.2 3.3 X2X X6Effect - 0.08 x2x3 U.**7 15.0 6.5 - 2.2 + 17.5 15.3 X X XX,Effect +0.38 1 = X1X2X3 1+.85 165.60 1

X. « Time: 1 minute (-) vs 1* minutes ( + ) 6.90 1

Xj - Wet (-) vs Dry (+) Flux 0.28 1 X, =» Vacuum Treatment (-) vs No Vacuum Treatment ( + ) 2.63 1 X, = Brazing Filler Metal A (-) vs Brazing Filler Metal B (+) 1U.51* 1 X3X6 1 X1X3X6 3.1+9 O.lU 1 X2X3X6 1 X1X2X3X6 2.93

Residual Sum 3U8.22 6U Y*B ABLf of Squares

THE I M I Mil TE (1) (LEFT) 4 MINUTES (4) (RI6HT

STATE Of FlUX DRY (D) CSOTTOM) IET (f) (TOP) g (Effect) « 20 (Effectf •Sum of Squares (Effect) VACUUM TREATMENT AFTER BRIGHT DIPPING NO (AT) (FRONT) TES (») (BACK)

BRAZING ALLOT METAL A (BOTTOM READING) 8 (TOP READING)

Table A3 Statistically Significant Effects Variable Lesser Embrittlement At

1 Time 1 minute

3 Wet or Dry Flux Wet Flux 6 Brazing Filler Metal Brazing Filler A vs B Metal B

1 Time 1 minute

5 Presence of Flux vs No Flux No FlUX

6 Brazing Filler Metal Brazing Filler A vs B Metal-B

l£ Time-Brazing Alloy See Text Interaction

1 Time 1 minute

6 Brazing Filler Metal Brazing Filler A vsB Metal B

Fig. 5 — Suggested "four dimensional plot" of Table A1 1 Time 1 minute

To the specific question "Is the time-brazing filler metal interaction in random draws from F- gu distribution or even among 18 draws if one limits

Table 5 significant?", one must answer yes. On the other hand, if it were attention to the two-variable interactions of Tables U-6. Indeed,

true that none of the 33 interactions of Tables h-6 are real, the value of considering the aggregate of interactions, the authors would conclude

lj.72 could be easily explained aa simply the largest value among 33 that none of them are real sources of embrittlement variation.

60-8 I FEBRUARY 1 975 Table A4 Table A6

Analysis of ' Variance for Variables 1 Analysis of Variance for Variables

1 - Time 1 - Time 2 - Kind of Flux 2 - Kind Of Flux 3 - Vacuum Treatment 1* - Body Oils 6 - Brazing Filler Metal 6 - Brazing Filler Metal (no body oils) (vacuum treatment)

Effect Variable Total DF EP_ •ii F Effect Variable Total DF GS K£ F 3 - 1*7.7 1 28.1+U 28.1*1* 5.23 1 1*8.5 1 29.U0 :29.1* 0 8.21. 1 71*.! 1 68.6U 68.61* 12.61 6 -127.3 1 202.57 2202.51 7 56.79 6 -115.1 1 165.60 165.60 30.53 2 - 0.9 1 0.01 0.01 0.00 2 - 19.7 1 U.85 lt.85 0.89 1* - 23.1 1 6.67 6.67 1.87 » - 6.5 1 0.53 0.53 0.10 16 - 13.3 1 2.21 2.21 0.62 36 - 3U.1 1 11*. 51* lit.51* 2.67 12 - 6.9 1 0.60 0.60 0.17 32 18.9 1 1*.1*7 It.U7 0.82 111 - 19.1 1 l*.56 U.56 1.28 16 - 23.5 1 6.90 6.90 1.27 62 6.5 1 0.53 0.53 0.15 12 - 29.3 1 10.73 10.73 1.97 61* 21.9 1 6.00 6.00 1.68 62 U.7 1 0.28 0.28 0.05 21* - 0.1 1 0.00 0.00 0.00 316 16.7 1 3.1*9 3.1*9 0.61* 162 - 10.3 1 1.33 1.33 0.37 312 19.7 1 U.85 1».85 0.89 161* - 6.5 1 0.53 0.53 0.15 362 3.3 1 O.ll* 0.1U 0.03 121* 2.7 1 0.09 O.09 0.03 162 - I**.5 1 2.63 2.63 0.1*8 62** - 1.5 1 0.03 0.03 0.01 1 3162 15.3 1 2.91* 2.93 0.5 * 1621* - 11.1 1 1.51* 1.51. 0.1.3 61. 3*8.32 5.1*1* (.1* 228.27 3-57 79 667.31 7" U8H.32

95 Percent Point of F(1,6U) • 3.99 95 Percent Point of F(l,61») . 3.99

Table A5 Table A7

Analysis of Variance for Variabl es Analysis of Variance for Variables 1 - Time 1 - Time 3 - Vacuum T reatment 3 - Vacuum Treatment 5 - Flux 1* - Body Oils 6 - Brazing Filler Metal (no flux, Brazing Filler Metal C) (no body oils)

Effect Effect Variable Total DF SS MS F Variable Total DF SS_ MS F

3 - 31*.6 1 11*.96 11*.96 3.87 3 6.6 1 1.09 1.09 2.1*3

1 1*1..6 1 21*.86 21*. 86 6.1*3 1 10.0 1 2.50 2.50 5.59

6 - 87.8 1 96.36 96.36 2U.93 1. 5.2 1 0.68 0.68 1.51

5 -130.6 1 213.20 213.30 55.16 31 3.2 1 0.26 0.26 0.57

31 - 12.6 1 1.98 1.98 0.51 3U 3.6 1 0.32 O.32 0.72

36 1.1+ 1 0.02 0.02 0.01 H; 7.8 1 1.52 1.52 3.1*0

35 - 5.8 1 0.1*2 0.1*2 0.11 311* 9.0 1 2.03 2.03 •+.53

16 - 38.2 1 18.21. 18.2U U.72 32 1>*. 32 0.1*5

15 - 0.2 1 0.00 0.00 0.00 39 22.71

65 22.6 1 6.38 6.38 1.65 95 Percent Point of F(l,32) = 1*.15 316 31*.2 1 11*. 62 11*. 62 3.78

315 - 25.8 1 8.32 8.32 2.15

365 32.2 1 12.96 12.96 3.35 APPENDIX II

165 - 0.2 1 0.00 0.00 0.00

BRAZING 3165 2.2 1 0.06 0.06 0.02 FILLED. MF.TAL A (all calculations are for 760" C or 11*00" F) a. ?.n + H 0 — ZnO + 61. 21*7.38 3.87 2 «2

79 659.80 AO' = AG° (Products) -AG" (Reaetants)

95 Percent Point of F(l,61*) = 3-99 = -58,085 - (-1*5,170) « -12,915 cal/mole

WELDING RESEARCH SUPPLEMENT! 61-s b. H2—2H d. AG" (Total) = -29,330 + 17,1*00 - 39,530

AG* = 17,1*00 cal/raole = -51,1*60 cal/mole

APPENDIX III

c. Cu?0 + 2H-»2Cu + lL0

AG* -AG± (HJO) -AG° (CU.,0) -AO" (2H) THE AMOUNT OF EMBRITTLEMENT CAUSED BY THE HYDROGEN IN BRAZING FILLER METAL A

BRAZE • -1*5,170 - (-23,01*0) - (17,1*00) !* sticks 0.0625" DIA X 1" Long (0.16 mm x 25.1* mm)

3 • -39,530 cal/mole DENSITY: 5.5 oz/cu in. (9.51 g/cm ) PROPORTION H_ BY WEIGHT: 0.2 ppm. d. AC" (Total) = AG" (a) +A.G" (b) +AG° (c) HYDROGEN PRESENT IN 1* STICKS OF BRAZING FILLER METAL

• -12,915 + 17,1*00 - 39,530 (0.03125) "Tt • 1" • 1* = 0.01227 cu in = 6.75 • 10" oz. = 1.925 grams of

braze filler metal " -35,01*5 cal/mole 0.2 ppm • 1.925 grams • 0.385 • 10" gr. of H^

7 3.85 • 10" gr. = 1.925 • 10"' moles of H? BRAZING FILLER METAL B MOLES OF COPPER IN A 0.006" ANNULAR RING AROUND A 0.188 DIAMETEH HOLE 1" LONG

a. Zn + H20—ZnO + Hj (0.09L + 0.006)2 - (0.09l*)2tr . 1 =. .001161* - 3.65 . IO"3 cu in.

3.65 • IO"3 cu in • 5.168 ox 1 cu in g/oz = 5.38 • IO"1 gr. AG" = AG" (Products) -AG" (Reaetants) 0.035

• -58,085 - (-1*5,170) = -12,915 cal/mole o.oooi* • 5.38 • io"-„-1l- .- 2.15 10" gr. of 0« = 6.72 • 10" moles of 0 Cd + H-0-"-CdO + H 2 2 The ratio of moles of hydrogen to oxygen when forming water is 2:1.

Assuming all the oxygen reacts to form H^O and that the oxygen initially AGC -AG" (Products) -AG° (Reaetants) in the form of copper oxides, is spread uniformly throughout the copper

- -7l*,500 - (-1*5,170) m -29,300 eal/mole matrix, we see that hydrogen from the braze can react with only 0.96 • 10 -7

The Cd - HpO reaction should be the dominant reaction. However, Cd moles of oxygen. 0.96 • 10 is only one-seventieth (0.011*3) of 6 mils or

tarnishes in air so that it may form a protective shield such that the 0.086 mils (0.31* microns).

reactions above may not progress past a certain point. Brazing filler metal has a hydrogen content of 1.8 ppm. Since its

density is identical to that of brazing filler metal A a direct comparison b. H2-+-2H can be made. The depth of embrittlement would be nine times that of

AG° = 17,1*00 cal/mole brazing alloy A or about 0.78 mils.

ETP Copper has a range of oxygen content from 0.02 to 0.08% oxygen. c. Cu?0 + H^-"- 2Cu + H,0 Therefore, even if the copper were low in oxygen, we would still observe

AG° > -39,530 cal/mole only 0.172 to I.56 mils embrittlement (0.68 to 6.1 microns).

Welding Power Handbook

This book provides a source of operating principles and useful data to the user of electric arc welding equipment. The operating details of specific pieces of welding equipment are not described. The handbook is divided into two parts. The first part discusses basic theory. The second part discusses practical applications of the fundamentals discussed. The first part reviews the fundamentals of elec­ tricity necessary for understanding the operation of arc welding systems. Rules of thumb are used where possible. A few of the rules of electrical engineering are bent, but not broken. In the second part, emphasis is placed on GMA and GTA welding systems. Some elementary knowledge of physics and electricity as taught in high school or as taught in vocational school, is helpful. The list price of the Welding Power Handbook is $6.00. Discounts: 25% to A and B members; 20% to bookstores, public libraries and schools; 15% to C and D members. Add 4% sales tax in Florida. Send your orders to American Welding Society, 2501 N.W. 7th St., Miami, Florida 33125.

62-s I FEBRUARY 1 975