Effect of Heat Treatment on the Microstructural Evolution and Mechanical Properties of NiW Medium/Heavy Alloys
The influence of various heat treatment temperatures on the microstructural evolution and mechanical properties of the cold-rolled Ni42W10ColMo alloy was studied.The results indicate that the tcp phases are transformed from σ phase to μ phase with the increase in heat treatment temperatures,and then transformed from μ phase to σ phase finally.The microstructure evolves from deformed dendrites to a uniform equiaxed grains.After heat treatment at 900 ℃,the precipitation phases are predominantly needle-like and blocky μ phases with a small quantity of granular μ phases.Recrystallization is also evident.After heat treatment at 1200 ℃,a substantial amount of granular σ phases is precipitated accompanying the completion of recrystallization.The extensive precipitation of tcp phases consumes a large number of W atoms,leading to a decrease in solid solution strengthening.The room temperature yield strength is decreased from 1564 MPa to 479 MPa after heat treatment at 1200 ℃,while the elongation is enhanced to 72.4%.The precipitation of larger-sized μ phases is adverse to ductility.The elongation of the alloy is only 7.1%after heat treatment at 900 ℃.