Effect of solution cooling rate on the γ′ precipitation behaviors of a Ni-base P/M superalloy

The effect of cooling rate on the cooling γ' precipitation behaviors was investigated in a Ni-base powder/metallurgy (P/M) superalloy (FGH4096). The empirical equations were established between the cooling rate and the average sizes of secondary and tertiary γ' precipitates within grains and tertiary γ' precipitates at grain boundaries, as well as the apparent width of grain boundaries. The results show that the average sizes of secondary or tertiary γ' precipitates are inversely correlated with the cooling rate. The shape of secondary γ' precipitates within grains changes from butterfly-like to spherical with the increase of cooling rate, but all the tertiaryγ' precipitates formed are spherical in shape. It is also found that tertiary γ' may be precipitated in the latter part of the cooling cycle only if the cooling rate is not faster than 4.3℃/s, and the apparent width of grain boundaries decreases linearly with the increase of cooling rate.