Influence of element Re on lattice misfits and stress rupture properties of single crystal nickel-based superalloys

Abstract

By means of the measurement of XRD curves and SEM, TEM observation, an investigation has been made into the influence of the element Re on lattice misfits and stress rupture properties of single crystal nickel-based superalloys. Results show that the bigger lattice parameters and misfit appear in 2% Re as-cast single crystal nickel-based superalloy due to the composition segregation and non-homogeneous distribution of the γ′ phase in size. After the alloy is fully heat treated, the cubical γ′ phase is coherently precipitated in the γ matrix phase, and the parameters and misfit of γ′, γ phases decreases slightly. During the stress/stress-free aging, the coarsening of γ′ phase occurs and the dislocation networks appear in the interfaces of the γ′/ γ phases, which increases slightly the parameters and misfit of γ′, γ phases. Compared to the γ matrix phase, the γ′ phase has a smaller thermal dilation coefficient due to the smaller thermal capacity and the stronger combined force between the atoms, which increases the misfit between the parameters of γ′ and γ phases in the alloy at the elevated temperature. The parameters of γ′, γ phases in the alloys increase with the element Re content, and compared with the parameter of γ phase, the one of γ′ phase increases to a bigger extent. Therefore, the misfits and mismatch stress of the γ′/ γ interfaces in the alloys decrease with the increase of the element Re content, which reduces the rafted rate of γ′ phase during stress aging and improves the stress rupture life of the alloys in the ranges of high temperature.