Precipitation of intersected plate-like γ′ phase in β and its effect on creep behavior of multiphase Ni₃Al-based intermetallic alloy

The precipitation and evolution of intersected plate-like γ′ (γ′_P) phase within interdendritic β during long-term aging and its relevant influence on the creep behavior of a multiphase Ni₃Al-based intermetallic alloy are investigated. Results show that the precipitation and growth of the γ′_P precipitates during 800 °C aging of original as-cast alloy are significantly rapid, which can be fully precipitated in 60 min to form the intersected morphology and continue to coarsen and grow during the extended aging and subsequent 800 °C creep processes. The γ′_P precipitates have the Bain orientation relationship (OR) of (100)γ′_P//(100)_β and [0-11]γ′_P//[001]_β with the interdendritic β-matrix. The precipitation of intersected γ′_P phase is sensitive to the elemental fluctuations in β-matrix, and the preceding high-temperature annealing treatment can significantly reduce the elemental inhomogenization and inhibit its generation within the interdendritic β. Precipitation of adequate intersected γ′_P phase can effectively inhibit the dislocation proliferation and crack initiation in the brittle interdendritic β during creep, resulted in the improved creep properties. Slightly rafted γ′ after long-term aging at 800 °C transitioned into R-type γ′-raft structure during creep at 800 °C/220 MPa, and can induce larger creep resistance than N-type γ′-raft structure.