Effect of recrystallisation on microstructural evolution and mechanical properties of single crystal nickel based superalloy CMSX-2 Part 2 - Creep behaviour of surface recrystallised single crystal

Abstract

Nickel based superalloy CMSX - 2 single crystal bars were shot peened to induce residual stresses at the surface. Full solutionising of shot peened specimens resulted in well developed recrystallised grains at the surface. Early initiation of surface cracks in recrystallised specimens at 982 ° C and 240 MPa in air did not reduce creep life, however, the life under vacuum was reduced. Early initiation of surface cracks on grain boundaries normal to the applied stress caused a relatively high creep rate in surface recrystallised specimens. Creep behaviour at 871 ° C, 500 MPa in air was similar to that at 982 ° C, 240 MPa under vacuum. Surface oxidation during creep at 982 ° C effectively hindered crack propagation, especially in recrystallised specimens.