Study on the Recrystallization Behavior of an as-Extruded PM Superalloy

The powder metallurgy (PM) nickel-base superalloy FGH96 was extruded at temperature from 1050°C to 1180°C,and the as-extruded samples in the extrusion temperature 1050°C were heat-treated at from 1000°C to 1100°C during 10min, 30min, 60min and 90min apart. The microstructure of recrystallization, γ' phase and growth behavior of grain were discussed. The results indicate that the extrusion temperature have a severely influence on the dynamic recrystallization and γ' phase behavior. The content and pattern of γ' phase is influenced by extrusion temperature and the big size of γ' phase in the grain boundary hinder effectively the growth of dynamic recrystallized grain. The degree of dynamic recrystallization is completed when the extrusion temperature increases. When the extrusion temperature reach 1100°C, the big size of γ' phase lie the grain boundary dissolves gradually and the grain grows obviously. As the heat temperature of as-extruded samples increases, the small size of γ' phase dissolves early and the degree of recrystallization is completed. When heat temperature reach 1080°C, the small size of γ' phase begin to dissolve and the recrystallization grain begins to grow, for the strain energy is given off and existence of interface energy. When heat temperature reach 1100°C, the recrystallization grain become uniform, for the pinning of big size of γ' phase. As the time of heat treatment elongate, the recrystallization grain size increase and the content of γ' phase decrease. When the heat temperature is 1080°C, the final microstructure is fine and uniform grain due to the pinning of big size of γ' phase. When the heat temperature is 1100°C, large of big size of γ' phase dissolve and the largest grain size reach 8μm. The nucleation and growth of recrystallization grain is influenced by small size of γ' phase and the fast growth of recrystallization grain is due to the big size of γ' phase in the grain boundary.