Solidification researches using transparent model materials — A review

Abstract

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 NH 4 Cl-H 2 O 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. transparent model materials, solidification, plastic crystal, dendritic growth Citation:Huang W D, Wang L L. Solidification researches using transparent model materials -A review.

Measurement of the capillary length for the dendritic growth of ammonium chloride

“…where D is the diffusion coefficient for NH 4 Cl in aqueous solution. The final result is that the radial growth velocity, dR/dt, is given by…”

“…It is important technologically because many metals and metal alloys solidify in dendritic patterns, but it is also of more general interest as one of the standard examples of pattern formation in a nonlinear, nonequilibrium system [1]. For reviews, see Boettinger et al [2], Glicksman and March [3], and Huang and Wang [4], In the standard model of diffusion limited crystal growth, there are two characteristic length scales [1]. One is the diffusion length l, given by l = 2D/v, where D is the relevant diffusion constant and v is interface velocity.…”

The initial growth of sidebranches in ammonium chloride dendrites

“…Dendrites are also more conveniently observed in the crystallization of transparent model compounds; see Akamatsu and Nguyen-Thi [6] and Huang and Wang [7] for overviews. Examples include succinonitrile and pivalic acid [2], rare gases, such as helium [8] and xenon [9], and some salts, such as ammonium bromide [10,11] and ammonium chloride [12,13,14,15,16].…”

Solid-liquid interface morphology of white carbide eutectic during directional solidification

“…It leads to the fact of important influence of these flaws on mechanical properties of metals and alloys. Nevertheless, because of the opacity of metallic materials, usually it is very difficult to conduct experimental study on the morphological details of a solidifying solid-liquid interface [11].…”