Microstructure of vapour-quenched TiMg alloys

A novel range of titanium-magnesium alloys were produced by a high rate evaporation and vapour-quenching route. Magnesium is virtually insoluble in titanium under equilibrium conditions, and this alloy combination is not possible by conventional ingot metallurgy owing to the high vapour pressure of magnesium, which boils at atmospheric pressure below the melting point of titanium. It was confirmed that each 1 wt.% addition of Mg reduced the density by approximately 1%. X-ray diffraction data showed that at least 28 wt. Mg was retained in solid solution. For the more dilute alloys (less than 10 wt.% Mg), heat treatment in air or in vacuum up to 700 °C was accompanied by a very substantial increase in hardness, which could not be explained in terms of oxygen absorption by the titanium lattice. Evidence is presented which suggests that the hardening is due to the precipitation of Mg or MgO.