Effect of heat treatment on the microstructural evolution and mechanical properties of NiW medium/heavy alloys

Abstract:

The influence of various heat treatment temperatures on the microstructural evolution and mechanical properties of the cold-rolled Ni42W10Co1Mo alloy was studied. The results indicated that the TCP phases transformed from σ phase to μ phase with the increase of heat treatment temperatures, and then transformed from μ phase to σ phase finnaly. The microstructure evolved from deformed dendrites to a uniform equiaxed grains. After heat treatment at 900°C, the precipitation phases are predominantly needle-like and blocky μ phases, with a small quantity of granular μ phases. Recrystallization was also evident. After heat treatment at 1200°C, a substantial amount of granular σ phases precipitated accompanying the completion of recrystallization. The extensive precipitation of TCP phases consumed a large amount of W element leading to a decrease of solid solution strengthening. The room temperature yield strength was decreased from 1564 MPa to 479 MPa after heat treatment at 1200°C, while, the elongation was enhanced to 72.4%. The precipitation of larger-sized μ phases was adversely to ductility, in contrast to the smaller-sized σ phases impeded crack propagation and enhcaned the ductility.