Electrodeposited tin-nickel thermal stability

Electrodeposited tin-nickel thermal stability

Scripta METALLURGICA Vol. Ii, pp, 301-304, 1977 Printed in the United States Pergamon Press, Inc. ELECTRODEPOSITED TIN-NICKEL THERMAL STABILITY C...

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Scripta METALLURGICA

Vol. Ii, pp, 301-304, 1977 Printed in the United States

Pergamon Press, Inc.

ELECTRODEPOSITED TIN-NICKEL THERMAL STABILITY

C. F. Hornig and J. F. Bohland Western Electric Company, Incoroorated North Andover, Massachusetts 01845

(Received December 6, 1976) (Revised January 25, 1977) Introduction Heating is known to transform electrodeposited tin-nickel, NiSn, to Ni~Sn2 and Ni3Sn4. Rooksby (1) reported that l h at 400°C transformed the alloy to Ni3Sn2-and Ni3Sn4. Following the early work of Rooksby, Cuthbertson, Parkinson, and Rooksby (2) reported that heating above 300°C produced a mixture of Ni3Sn2 and Ni3Sn4. Smart and Robins (3) investiqating the structural s t a b i l i t y of tin-nickel electrodeposits reported the alloy to remain single phase, NiSn, to at least 500°C but to transform at 700°C into a mixture of two phases, Ni3Sn2 and Ni3Sn4. Subsequent to Snort and Robins, Dutta and Clark (4) reported the electrodeposited alloy to be unstable at 250°C and noted that the extent of decomposition increased sharply from 300°C upwards. Thus, although several studies of tin-nickel electrodeposit thermal s t a b i l i t y have been conducted in the past, there is uncertainty as to the temperature at which transformation occurs and to what extent the alloy transforms to Ni3Sn2 and Ni3Sn4. In this communication we investigate the solid phase transformation of tin-nickel and ascertain i f partial transformation to a multiphase structure can occur at temperatures well below that necessary for a ma.ior transformation. The investigation consisted of heatinq powdered tin-nickel electrodeposits in a vacuum for times up to five months and at temperatures to 600°C. The tin-nickel phase was determined immediately after electrodeposition and followinq heat treatment using an x-ray diffraction technique. In addition we determined the phase of a tin-nickel electrodeposit believed to have been aged at least ten years at room temperature. Experimental Using the Tin Research~Institute plating solution (5) at 70° + 3°C, -O°C, we electroplated tin-nickel at 2.1A/dm~ onto a stainless steel substrate. The poor adherence of electrodeposits to an inactive surface enabled removal of tin-nickel through bending of the stainless steel substrate. Flakes and silvers of tin-nickel obtained from flexing the passive stainless steel substrate were ground to a powder with a maximumdiameter of 0.075 mm. Vials containing 0.2 mkg of tin-nickel powder were sealed in a vacuum at approximately 1.33 x lO-~ Pa. Isothermally heating the vials at the temperatures and for the times shown in Table l , the authors observed the furnace temperature to be constant within + l°C. An absolute error of ~ 2°C may be attributed to the inherent inaccuracies (6) oT chromel-alumel thermocouples. To determine the crystallographic structure, tin-nickel powers were mixed with a binder, smeared onto the surface of a glass slide, and placed in a goniometer. The x-ray source was a copper target excited by an electron beamof potential 40kV and 40 mA. A carbon crystal monochromator f i l t e r e d the copper K~ radiation. Results X-ray fluorescent analysis determined the tin-nickel composition at 66.9 wt. % tin and 33.1 wt. %nickel. Fresh electrodeposited tin-nickel and the tin-nickel electrodeposit believed to have been aged at least ten years at room temperature were observed to have the single phase, NiSn, d spacings as shown in Table 2. Electrodeposited tin-nickel, transformed completely to the alloys Ni3Sn2 and Ni3Sn4 when heated at 300°C for 20 h and 400°C, 500°C, and 600°C for l h. The d spacings for these transformations are shown in Table 2. Electrodeposits heat treated at 200°C and 300°C for l h were a mixture of NiSn and Ni3Sn4

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as shown by the d spacings tabulated in Table 2. Subsequentheating of a 200°C specimen for 4 h produced no detectable change in the structure from that of the tin-nickel electrodeposit heated l h at 200°C. Electrodeposits heated at 150°C, 125°C, lO0°C, and 50°C for 3.5 x lO3 h partially transformed to Ni3Sn4 as shown in Table 2. Over the temperature range from 50°C to 200°C a small and almost constant amount of NiSn transformed to Ni3Sn4. A paramount but not complete solid phase transformation to Ni3Sn2 and Ni3Sn4 occurred after 20 hours at 300:C. The sinqle phase NiSn heated at and'above 400°C transformed completely to Ni3Sn2 and Ni3Sn4. Figure l contrasts the d snacing x-ray intensities for transformation from 50°C to 500°C and illustrates the d spacing x-ray intensities associated with the fresh and ten year room temperature aqed tin-nickel electrodeposit. Discussion The transformation of the single phase tin-nickel to the multiphase structure as observed at and above 300°C corresponds with the findings reported by Dutta and Clarke (4). The x-ray intensity differences between the observed d spacings and the standards, (1,2,7) as shown inTable 2 indicated preferred orientation of the electrodeposit grain structure. This preferred orientation and the similarity between the ma.ior d values for Ni3Sn2 and NiSn may have prevented identification of the Ni3Sn2 phase in the tin-nickel electrodeposits isothermally heated a~ 200°C and 300°C for l h and those electrodeposits heated from 50°C to 150°C for 3.5 x lOj h. Transformations to the multiphase structure after 3.5 x lO3 h at temperatures from 50°C to 150°C supports the analysis by Dutta and Clarke (4) that the structural change to a multiphase alloy is accomplished by diffusion and that the lack of detectable change in a short time may well be evidence of the slow rate of the process. The weak intensity of the Ni3Sn4 2.67 A d spacing associated with those NiSn electrodeposits isothermally heated from 50°C to 150°C indicated a minimal amount of Ni3Sn4 phase. In contrasting the amount of NiSn, Ni3Sn2 and Ni3Sn4 phases present in the electrodeposits isothermally heated from 500C to 600°C, we selected only those x-ray diffraction peaks which could be attributed to one phase and which appeared consistently over a range of heat treatments. Conclusions Electrodeposited tin-nickel undergoes a ma.ior transformation to Ni3Sn2 and Ni3Sn4 when isothermally heated at 300°C for at least 20 h and when isothermally heated at and above 400°C for at least l h. Isothermal heating at 200°C for l h transforms single phase tin nickel to a mixture of NiSn, Ni3Sn4 and possibly Ni3Sn2. A small amount of NiSn transforms to Ni3Sn4 and possibly Ni3Sn2 at temperatures from 500C to 150°C for 3.5 x lO3 h. Electrodeposited tin-nickel is stable at room temperatures for at least ten years. Acknowledgements The authors thank Dr. M. Antler and P. T. Woodberry for their constructive comments during the course of this investigation. References I. 2. ~. 4, 5. 6. 7.

H. P. Rooksby, J. Electrodepositors' Tech. Soc., 2_7_~153(1951). J. W. Cuthbertson,"N. Parkinson,'-and H. P. 'Rooksby, J. Electrochemical Soc., lO0 I07 (1953). R. F, Smart and D. A. Robins, Trans, Inst. Met, Fin,, 37, I08 (1960). P, K, Durra and M, Clarke, Trans', Inst, Met, Fin,/46,~O (1968). Electroplated Tin,NiCkeIAlioy, ~Tin Research Institut-e, Publication 235, 4th ed., Ig62. Leeds & Northrup 1973 General Catalog, Leeds & Northrup Co., North Wales, Pa., 1973; p. 85. Nowotnyand Schubert, Metallforschun 9, BD, l , I/2, 23 (1946).

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FIGURE I

X-Ray Intensity Ratio vs. Heat Treatment 100

2.94~ [~l 2.08~ NiSn 2.68~ Ni3Sn4

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TABLE l Heat Treatment of I n i t i a l Single Phase Tin-Nickel Temperature 600% 500°C 400°C 300°C 300% 200°C 200% 150°C 125°C lO0°C 50°C

Time l h l h l h l h 20 h l h 4 h 3.5 x 3.5 x 3.5 x 3.5 x

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