Thermodynamic analysis of carbide precipitation and effect of its configuration on creep properties of FGH95 powder nickel-based superalloy

By means of heat treatment at various regimes, creep property measurement, microstructure observation and thermodynamic analysis, the precipitation behaviors of carbides and effect of its configuration on the creep properties of FGH95 alloy are investigated. Results show that after solution treated at 1155 ℃ and fully heat treatment, the microstructure of alloy consists of fine γ' phase, γ matrix, (Nb, Ti)C and M23C6 carbides. The excellent creep life of alloy at 1034 MPa/650 ℃ is attributed to some fine carbide particles precipitating along boundaries to restrain dislocations and boundaries slipping. Moreover, the boundaries appear in the original PPB regions of alloy after solution treated at 1165 ℃, and the carbide films are continuously distributed along boundaries to weaken the bonding strength between grains, which are thought to be the main reason of the alloy displaying a weakest creep resistance. By means of thermodynamic calculation, the precipitation temperatures of NbC and TiC carbides are determined to be 1080 ℃ and 807 ℃, respectively. Compared to (Nb,Ti)C carbide, the reason of no WC carbide precipitated in the alloy is attributed to its smaller driving force of nucleation.