B22-P-17Evolution of the MC carbide in Nickel-base single crystal superalloy exposing at 950 °C

Abstract

Nickel-base single crystal superalloy have been largly used in the turbine blade [ 1 ]. Its microstructure is consisting of the network structure y/γ' matrix and MC carbide after heat treatment for the C element containing Nickel-base single crystal superalloy [ 2 ]. The MC carbide is rich in heavy elements and serves as the site for micro-crack nucleation [ 3 ]. Therefore, it is important to study the evolution of MC carbide to help understanding of the failure mechanizem of superalloy. Figure 1 shows the TEM images of three carbides formed during exposure at 950 °C.The MC carbide was formed after heat treatment, the M 6 C and M 23 C 6 carbides precipitated after 100 h and 900 h exposure, respectively. Precipitation of the M 6 C and M 23 C 6 was accompanied by gradually disappear of the MC carbide. As the exposure time increases to 3000 h, only the M 23 C 6 carbide left. The evolution of the carbide is suggest to be that the MC carbide will degrade to M 6 C and M 23 C 6 carbides and the new formed M 6 C carbide also will degrade to M 23 C 6 carbide.