Precipitation behavior of μ phase and creep rupture in single crystal superalloy CMSX-4

Precipitation behavior of a topologically close packed (TCP) μ phase as well as its role during the creep deformation in single crystal superalloy CMSX-4 have been investigated. The μ particles nucleated and grew based on low index planes of both the μ phase ({1 1 2¯ 0} and {1 0 1¯ 0}) and the matrix ({1 1 0}, {0 0 1} or {1 1 1} and {1 1 2}) by epitaxial growth toward 〈0 0 0 1〉μ or 〈1 1 0〉γ directions, which predominantly resulted in a rod-like morphology. Interestingly, composition of these rod-like μ particles varied with the ratio of Ni/(W + Re) due to the different diffusion rates of these elements in the matrix during thermal exposure. Moreover, the γ′ evolution played an important role in the precipitation behavior and the fracture behavior of the μ phase. The rod-like μ particles were not fractured by stress concentration, as they were surrounded by the γ′ envelope.

► Precipitation behavior of a rod-like μ phase was investigated in the alloy CMSX-4. ► The μ particles nucleate and grow based on low index planes of μ phase and matrix. ► Epitaxial growth resulted in the predominantly rod-like morphology. ► Role of the μ particles during the creep deformation is dependent on the creep rate. ► The rod-like μ particles were not fractured by stress concentration. ► Composition of the μ particles varied a lot by changing the ratio of Ni/(W + Re).