Effect of phosphorus segregation on carbides and creep damage of Ni–Fe-based GH984G alloy

Abstract

The effect of phosphorus segregation on carbides and creep damage of Ni–Fe based GH984G alloy, for the application of advanced ultra-super critical (A-USC) power plant, were investigated under the creep condition of 750 °C and 200 MPa. The results indicate that the primary precipitates of GH984G alloy are MC, M23C6 and γ′ after standard heat treatment. P-doping has no effect on the grain size, γ′ size and morphology. Nevertheless, P atoms segregate at the grain boundaries and around the MC carbides, resulting in a change in the morphology of M23C6 carbides at grain boundary from film-like to granular and a decrease in the density and area percentage of MC carbides. The creep behavior of GH984G alloy at 750 °C/200 MPa changes significantly after P doping and the creep properties (creep life and elongation) are optimized with the increasing P content. The damage feature is microcrack at grain boundaries for P-free alloy, while the creep cavities in P-doped alloy. The fracture mode changes from intergranular fracture to transgranular fracture with the increasing P doping for GH984G alloy after creep at 750 °C/200 MPa. The optimizing of creep properties and transformation of fracture mode of GH984G alloys after P doping are mainly attributed to increase of grain boundary cohesion and the change of carbides caused by the P segregation behaviors during creep process.

Keywords

• Phosphorus segregation
• GH984G alloy
• Carbide
• Creep damage