Effect of pre-strain on microstructural evolution during thermal exposure of single crystal superalloy CMSX-4

Compressive and tensile pre-strains at room temperature were induced in the second generation single crystal superalloy CMSX-4 fully heat treated. Both compressive and tensile pre-strain generated shear bands in the single crystal CMSX-4. Thermal exposure for 10 h at 950 °C on the pre-strained single crystal CMSX-4 developed preferential coarsening of γ' particles along the shear bands. γ' particles on the shear band gradually invaded γ channel. Finally, the γ channels along the shear band disappeared. TCP-like particles appeared at the expense of γ channel disappearance. However, thermal exposure for 10 h of the normal single crystal CMSX-4 did not develop TCP precipitation or preferential coarsening of γ' particles. Thermal exposure for 100 h of pre-strained CMSX-4 developed preferential coarsening of γ' and TCP phase particles along the shear bands as well as coarsening of γ' particles in the matrix.