Microstructure evolution and mechanical property characterization of a nickel-based superalloy at the mesoscopic scale

Nickel-based superalloys have become the critical materials of micro-parts depending on outstanding mechanical properties. The effects of the grain size and precipitates on the mechanical properties at the mesoscopic scale are difficult to be revealed using conventional macroscopic material constitutive models. In the present study, the microstructure evolution of the γ″ phase and the tensile mechanical properties of a nickel-based superalloy at the mesoscopic scale were investigated systematically. Three variants of γ″ phases precipitated corresponding to [00], [00] and [001] orientations of the matrix γ phase. The quantitative statistics results showed that as the aging time increases, the particle size and volume fraction of the γ″ phase increase. As the grain size increases, the flow stress decreases due to the dwindling of grain boundary strengthening. Furthermore, the precipitation strengthening of γ″ and γ′ phases induces the increase of flow stress. An important conclusion is drawn that the size effect at the mesoscopic scale depends not only on the sample size and grain size but also on the particle size and volume fraction of the precipitates. The established constitutive model which considers grain boundary strengthening, precipitation strengthening and solid solution strengthening can accurately describe the flow stress characteristics of nickel-based superalloys at the mesoscopic scale.