Formation and evolution behavior of M6C carbide in a Ni-W-Cr superalloy

The carbide formation and evolution of a new Ni-26W-6Cr (wt.%) superalloy for the 800 °C molten salt reactor (MSR) was investigated by homogenization heat treatment tests and the effect of carbide characteristics on the plastic deformation behavior was further investigated by isothermal simulated tensile tests. The plastic deformation properties of Ni-26W-6Cr superalloys are associated with the morphological characteristics and distribution of carbides. During homogenization at 1220 °C, a unique phenomenon was discovered, that is, the precipitation of the acicular carbide. The XRD, TEM and EBSD results show that this acicular carbide is distributed along the particular crystal plane of the γ matrix. Based on crystallographic theory, there is no obvious orientation relationship between the carbide and the γ matrix, which is prone to cracking along the carbide/γ interface during deformation. After homogenization at 1220 °C for 48 h, the acicular M6C carbides dissolved and the discrete granular M6C carbides distributed diffusely at the grain boundaries can relieve stress concentration and strengthen the grain boundaries, reducing the deformation resistance of the alloy, effectively inhibiting grain boundary slip and thus inhibiting crack propagation, and improving the tensile strength and plasticity of the material.