Investigation on peritectic solidification in Sn-Ni peritectic alloys through in-situ observation

Abstract

The solidification of Sn-Ni peritectic alloys in which both the primary Ni3Sn2 and peritectic Ni3Sn4 phases were intermetallic compound phases (IMCs) with narrow solubility ranges was investigated through confocal laser scanning microscope. Analysis on the interface migration at different cooling rates shows that the rate of peritectic reaction is much smaller than previous reports, and the growth of peritectic phase is mainly attributed to direct precipitation from the melt in Sn-Ni alloy after peritectic reaction. In addition, different from other peritectic alloys where the solidified phases are solid solution phases, the "step" growth of both Ni3Sn2 and Ni3Sn4 phases was observed. The dependences of the step thickness on both the cooling rate and solidification time were measured, which shows that the step thicknesses of both phases gradually decrease as solidification proceeds. This was confirmed to be attributed to the difference between the actual and equilibrium melt concentrations during solidification. In addition, the increase of the normal growth velocity of Ni3Sn4 phase with increasing cooling rate was also proved through both the experimental observation and quantitative prediction.