Solidification researches using transparent model materials - A review

A review is given in the paper for solidification researches with transparent model materials. The effective experimental method was first proposed by Jackson and Hunt in 1965. The transparent model materials for solidification researches are a kind of non-faceted crystals known as plastic crystals or globular molecules, which have very low entropy of melting as that of metals. According to Jackson's theory proposed in 1958, entropy of phase transformation will determine whether the phase interface morphology is smooth or rough in atomic scale, which will lead to faceted or nonfacted phase interface in microscopic and macroscopic scales. Succinonitrile (SCN) and its alloys with water, ethanol, acetone, and NH4Cl-H2O solution are most commonly used as transparent model materials for solidification researches of dendritic growth, anisotropy of solid-liquid interfacial energy, crystal nucleation, crystal grain formation, directional solidification, eutectic and peritectic solidification, solidification defects formation such as bubble, hot tearing, etc. Among these researches, the most impressive work was the critical test of dendritic growth theories with high purity succinonitrile by Glicksman et al., which gave positive answer to the Ivantsov's analysis and negative answer to the ad hoc condition of the maximum velocity hypothesis. The future researches with transparent model materials could be suggested in three aspects: 1) accurate measurement of material properties and alloy phase diagrams in more plastic crystals, especially to find more transparent eutectic and peritectic alloys; 2) accurate measurement of the grain boundary groove shape to obtain precise data of the anisotropy parameters of the interfacial free energy in transparent model materials; 3) to get clear pictures of solidification processes with morphology details in a relatively large area, with continuous movement of liquid and particles, in order to give experimental support to numerical simulations aimming at accurate description of microstructure formation during solidification of multicomponent alloys under complex conditions of real casting and welding processes.