Effect of recrystallisation on microstructural evolution and mechanical properties of single crystal nickel base superalloy CMSX-2 - Part 1 - Microstructural evolution during recrystallisation of single crystal

Nickel base superalloy CMSX-2 single crystal bars were shot peened to induce surface residual stresses. Partial solutionising at 1300degreesC revealed a relationship between dissolution of the gamma' phase into the matrix and recrystallisation. Recrystallisation occurred with dissolution of gamma' phase in the dendritic core at 1300degreesC. Recrystallisation had preferentially begun at the dendritic core exposed at the shot peened surface and then gradually proceeded to the interdendritic regions. Phases more resistant to dissolution such as the coarse gamma' particles and the gamma-gamma' eutectic phase in the interdendritic region dissolved into the matrix with recrystallisation, even at 1300degreesC, which is lower than the solutionising temperature of the alloy. Residual stresses assisted dissolution of the existing phases. The recrystallised grains grew preferentially in the dendritic core where rapid dissolution of gamma' phase occurred. The growth of the recrystallised grains was impeded by the coarse gamma' particles and the gamma-gamma' eutectic phase in the interdendritic region. Full solutionising of the shot peened specimens resulted in well developed recrystallised grains at the surface.