Influence of γ′ precipitate morphology on the creep property of a directionally solidified nickel-base superalloy

The effect of γ′ precipitates of different morphologies and sizes on the creep property of DZ951 alloy was investigated. Standard heat treatment (SHT) alloy has regularly aligned cubic γ′ phase and the γ′ size is about 300 nm. γ′ phase of HT1 alloy has the shape of cuboid and the size of 880 nm. HT2 alloy has γ′ precipitates of different morphologies and sizes. There is spherical γ′ phase of 150 nm in size between γ′ raftings. SHT and HT1 alloys have the same creep properties and small steady creep rates at 1040 °C/100 MPa, which is attributed to forming perfect rafting and regular dislocation networks in the γ/γ′ interface during creep test. The deformation structure of HT2 alloy is heterogeneous due to γ′ precipitates of different morphologies and sizes. It is easy for the dislocation networks to breakup because of high stress made by uneven deformation structure, which results in the short secondary stage and long tertiary stage at 1040 °C/100 MPa. SHT alloy is strengthened by tangling of dislocations each other without forming regular dislocation networks and perfect rafting structure at 850 °C/400 MPa, which results in high creep rate and short steady creep time. The low creep properties of HT1 and HT2 alloys arise from the heterogeneous deformation structure during creep test at 850 °C/400 MPa.