Effects of Co on microstructure evolution of a 4th generation nickel-based single crystal superalloys

For further composition optimization, the microstructure evolution of the fourth-generation nickel-based single crystal superalloys, which contains different Co (Cobalt) additions, is studied at three thermal exposure temperatures. Based on Lifshitz, Slyozov and Wagnerz (LSW) theory and trans-interface diffusion-controlled (TIDC) theory, the effects of Co content and aging temperatures on coarsening rate of gamma ' phase are investigated in detail. The results show that the diffusion coefficient of solute is accelerated, but the gamma/gamma ' interfacial energy decreases with the addition of Co, thus changing the coarsening rate. Furthermore, the thermodynamic equilibrium solubility difference of elements between gamma ' and gamma, and the segregation of elements at the gamma/gamma ' interface are alleviated with increase of Co, resulting in the suppression of TCP phase after long-time thermal exposure, which guides the economical design of nickel-based single crystal superalloys.