Génétique humaine et Embryologie

The Affect of Liquid Ordering and its Inheritance on the Phase Transformation of Mg-Al-Ca Alloys

Abstract

Tim David

It has long been an aim to attain desired mechanical characteristics in alloys by controlling phase formation, particularly in intricate multi-phase alloys. In fact, the composition of the liquid influences the nucleation of competing crystalline phases during solidification. We use ab initio molecular dynamics simulations (AIMD) to disclose the liquid structure of Mg-Al-Ca alloys and investigate its influence on the change of Ca-containing Laves phase from Al2Ca to Mg2Ca when the Ca/Al ratio (rCa/Al) increases. In terms of the local arranging environment and polyhedra connection schemes, there is structural similarity between the liquid and crystalline phases. As shown by the topological and chemical short-range order arising from liquid, the forming signature of Mg2Ca ascends monotonically with increasing rCa/Al. However, at the crossover of rCa/Al = 0.74, the Al2Ca crystal-like order increases at first and subsequently decreases, according to the observed composition of the phase transition from Al2Ca to Mg2Ca. The tight packing of atomic configurations and preferential bonding of chemical species in both liquid and solid are the origins of phase change across various compositions.