Rapid solidification of undercooled Ni-15%Cu （mole fraction） alloy was studied using glass fluxing and cyclic superheating. To show the effect of cooling history on the microstrucyure and microtexture evolution, the as-solidified samples were either cooled naturally or quenched into water after recalescence. At low undercooling, grain-refined microstructure has a random texture and a highly oriented texture without annealing twins for the case of naturally cooling and quenching, respectively. At high undercooling, a fully random texture as well as a number of annealing twins are observed, and recrystallization and grain growth independently happen on the cooling history. Fluid flow and recrystallization play an important role in the microtexture formation for grain refinement at both low and high undercooling.
Solid-state phase transformation plays an important role in adjusting the microstructure and thus tuning the properties of materials. A general modular, analytical model has been widely applied to describe the kinetics of solid-state phase transformation involving nucleation, growth and impingement; the basic conception for iso-kinetics which constitutes a physical foundation for the kinetic models or recipes can be extended by the analytical model. Applying the model, the evolution of kinetic parameters is an effective tool for describing the crystallization of enormous amorphous alloys. In order to further improve the effectiveness of this kinetic model, recently, the recipes and the model fitting procedures were extended, with more factors （e.g., anisotropic growth, soft impingement, and thermodynamic driving force） taken into consideration in the modified models. The recent development in the field of analytical model suggests that it is a general, flexible and open kinetic model for describing the solid-state phase transformation kinetics.
The effect of cooling rate of the solidification process on the following solution heat treatment of A356 alloy was investigated,where the cooling rates of 96 K/s and 3 K/s were obtained by the step-like metal mold.Then the eutectic silicon morphology evolution and tensile properties of the alloy samples were observed and analyzed after solution heat treatment at 540 °C for different time.The results show that the high cooling rate of the solidification process can not only reduce the solid solution heat treatment time to rapidly modify the eutectic silicon morphology,but also improve the alloy tensile properties.Specially,it is found that the disintegration,the spheroidization and coarsening of eutectic silicon of A356 alloy are completed during solution heat treatment through two stages,i.e.,at first,the disintegration and spheroidization of the eutectic silicon mainly takes place,then the eutectic silicon will coarsen.
