Cooling γ′ precipitation behavior and strengthening in powder metallurgy superalloy FGH4096

Two cooling schemes (continuous cooling and interrupted cooling tests) were applied to investigate the cooling γ′ precipitation behavior in powder metallurgy superalloy FGH4096. The effect of cooling rate on cooling γ′ precipitation and the development of γ′ precipitates during cooling process were involved in this study. The ultimate tensile strength (UTS) of the specimens in various cooling circumstances was tested. The experiential equations were obtained between the average sizes of secondary and tertiary γ′ precipitates, the strength, and cooling rate. The results show that they are inversely correlated with the cooling rate as well as the grain boundary changes from serrated to straight, the shape of secondary γ′ precipitates changes from irregular cuboidal to spherical, while the formed tertiary γ′ precipitates are always spherical. The interrupted cooling tests show that the average size of secondary γ′ precipitates increases as a linear function of interrupt temperature for a fixed cooling rate of 24°C/min. The strength first decreases and then increases against interrupt temperature, which is fundamentally caused by the multistage nucleation of γ′ precipitates during cooling process.