Influence of Processing Parameters on the Solidification Behavior of Single-Crystal CMSX-4 Superalloy

The microstructural evolution of a superalloy, single-crystal CMSX-4 solidified at different withdrawal rates was investigated using a directional solidification quenching method. Analyses of the cross-sections within mushy zones generated the evolution of the solid volume fractions (f _s) during the reduction in the temperature and the solidification sequences. At the withdrawal rate of 0.3 mm min⁻¹, f _s increases by about 81 pct within the first 23 pct of the solidification interval, whereas it increases by about 64 pct at the withdrawal rate of 0.7 mm min⁻¹. The Bower–Brody–Flemings model can characterize the evolution tendency of f _s curve at the lower withdrawal rate, while it can not only describe the changing tendency of f _s, but also precisely predict the f _s values at higher withdrawal rate. With increasing withdrawal rate, the solidification intervals of the γ dendrite and γ/γ′ eutectics are increased. In addition to this, the forming site of the γ/γ′ eutectic at the lower withdrawal rate lags behind that at the higher withdrawal rate. At both the withdrawal rates the solidification of the γ/γ′ eutectic islands commences with the γ/γ′ core formed on the surface of the γ dendrites, then progressed spatially and developed the coarse γ/γ′ structure.