Precipitation evolution in Cux[Ni3Cr1] spinodal alloys under mismatch control

Abstract Cu Ni Cr alloys have a typical spinodal decomposition structure. However, a systematic investigation of the correlation between the mismatch of the two decomposition phases, Cu-rich (γ 1 ) and Ni-rich (γ 2 ), and the γ 2 morphology is lacking. In this study, the microstructure evolution of Cux[Ni3Cr1] (x = 1, 2, 3, 4, 5, 7, 9, and 12) alloys was investigated over a wide composition range. The results show that mismatch significantly affects the shape of the γ 2 precipitates. The γ 2 phase is cubic when the mismatch degree ( η ) is in the range 0.62%–0.75% and lath-shaped when η is in the range 1.08%–1.35%. With increasing Cu content, the proportion of the lath-shaped γ 2 phase decreases and that of the cubic γ 2 phase continuously increases. Cubic precipitates enhance the alloy strength, while lath-shaped precipitates show better corrosion resistance owing to their high packing density. Therefore, an appropriate x can be chosen according to the actual service conditions. In addition, the Cr state affects the microstructure and performance of the alloys. Cr in the solid solution state promotes spinodal decomposition, while a large amount of Cr-rich precipitates at the grain boundaries has a negative effect on the mechanical performance.