Microstructure and Recrystallization Behavior of an as-Extruded PM Nickel-Base Superalloy

The powder metallurgy (PM) nickel-base superalloy GH720 was extruded at 1100°C and the as-extruded samples were treated at 1110°C during 10min, 20min and 30min apart. The microstructure and recrystallization behavior of as-extruded alloy GH720 were discussed. The results indicate that there are two different types of γ' phases: primary γ' phase is mainly distributed on the grain boundary with an average size ranging from 0.3 to 0.5μm and dissolves partially at 1110°C during 30min, whereas the secondary γ' phase is distributed inside the grains with an average size of 50nm and dissolves largely at 1110°C during 30min. Recrystallization mechanism is subgrain nucleation when as-extruded GH720 is treated at 1110°C at which a lot of γ' phase exist. γ' phase inhibits growth of recrystallized grain availably and the uniform, fine and equiaxed grains in GH720 were formed during the extrusion and following heat treatment process.