Long-term thermal exposure responses of the microstructure and properties of a cast Ni-base superalloy

Microstructural evolution and microstructure-property relationship during long-term thermal exposure in K446 alloy are investigated in detail. The coarsening rate of γ′ precipitates increases with the rise of exposure temperature, yet decreases with the increment of exposure time. Primary MC carbides present an excellent stability and decompose to a tiny degree by two reaction forms, which have an insignificant influence on the properties. TCP-μ phase precipitates from the supersaturated matrix in the forms of needles and granules and experiences a remarkable evolution with prolonged exposure; the μ phase near the grain boundaries (GBs) evolves slower than that within the grains due to the inhomogeneous distribution of elements. In addition, the precipitation of μ phase is determined to be more detrimental to the mechanical properties than the γ′ coarsening in the present alloy.