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 gamma dendrite and gamma/gamma' eutectics are increased. In addition to this, the forming site of the gamma/gamma' eutectic at the lower withdrawal rate lags behind that at the higher withdrawal rate. At both the withdrawal rates the solidification of the gamma/gamma' eutectic islands commences with the gamma/gamma' core formed on the surface of the gamma dendrites, then progressed spatially and developed the coarse gamma/gamma' structure.