Microstructure and crystal structure of an equimolar Mg-Ti alloy processed by Simoloyer high-energy ball mill

Abstract

The solid solubility of 50-50 at.% Mg-Ti powder mixtures was achieved by means of high energy ball milling in a Simoloyer equipment. XRD and HRTEM analyses revealed the existence of FCC and BCC matrix of Ti solid solution in Mg containing small amounts of an HCP Ti-rich phase formed after milling for 48 and 72h, respectively at 800 rpm. An intermediate FCC solid solution of Ti in Mg was identified in powders milled for 24h or less. The chemical composition of the matrix products extended from Ti56:Mg44 to Ti50:Mg50, which is close to the targeted equimolar ratio. XRD analysis of the structure suggested that the release of the lattice strain energy contributed to the driving force for transformation and solid solution between Mg and Ti after ball milling. Twinning was observed in Ti-rich crystallites at intermediate milling time. The twinning observed could be attributed to the deformation of Ti particles. However, in the Mg-Ti system, it might also indicate a strain induced martensitic transformation of the metastable ω-FCC into BCC product. The crystallite boundaries acted as preferential sites for the heterogeneous nucleation of the twins and for the formation of solid solution by release of the lattice strain energy.