Coarsening kinetics of γ′ phase in isothermal aged high Al content Ni–17 at.% Al alloy

Abstract

The morphology evolution and coarsening kinetics of γ′ phase in high Al content Ni–17 at.% Al alloy aged at 830 °C are studied by transmission electron microscopy (TEM) and hardness analysis. The γ′ phases evolve from the near-cuboidal to rectangular strips along [100] and [010] directions. There is synchronous increase of alloy microhardness and γ′ phase volume fraction in early stage, while the microhardness decreases after 24 h aging with the formation of coalescent γ′ phase. The precipitation process shows the early precipitation stage and the later coarsening stage with the distinct time exponent 0.082 and 0.251 of average particles radius, the strong elastic stain fields make the time exponents of average particles radius lower than 1/3 of Lifshitz-Slyozov-Wagner (LSW) theory. As aging time goes on, the particles size distribution (PSD) is widening, and the peak position moves from 1.0 to 0.9. The relationship between the coarsened γ′ phase and the alloy mechanical property is also revealed in this γ′ phase strengthened high Al content alloy.