MICROSTRUCTURE OF VAPOR-QUENCHED TI-MG ALLOYS

A novel range of titanium-magnesium alloys were produced by a high rat e evaporation and vapour-quenching route. Magnesium is virtually insol uble in titanium under equilibrium conditions, and this alloy combinat ion is not possible by conventional ingot metallurgy owing to the high vapour pressure of magnesium, which boils at atmospheric pressure bel ow the melting point of titanium. It was confirmed that each 1 wt.% ad dition of Mg reduced the density by approximately 1%. X-ray diffractio n 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 degrees C was accompanied by a very substan tial increase in hardness, which could not be explained in terms of ox ygen absorption by the titanium lattice. Evidence is presented which s uggests that the hardening is due to the precipitation of Mg or MgO.