Role and behaviour of μ phase during deformation of a nickel-based single crystal superalloy

The effect of the presence of variable amounts of the topologically closed packed (TCP) μ phase on the mechanical properties of the MC2 nickel-based single crystal superalloy has been investigated. It is shown that moderate amounts of needle-like μ particles do not affect the tensile properties or the impact strength at 25°C. The precipitates behave similarly to brittle short fibres in a ductile matrix, thus internal cracking occurs under stress rather than interfacial decohesion. For a higher amount of μ phase, precipitates are of smaller size and of globular shape, exhibiting a weaker interface with the γ/γ′ matrix, thus they are more prone to decohesion. By separating effects due to the μ phase from those due to the rafted γ/γ′ microstructure, it is shown that the low cycle fatigue (LCF) properties of MC2 alloy at 650 and 950°C are not affected by the presence of μ phase. Finally, some observations related to the behaviour of μ phase precipitates during high temperature creep are presented.