Ti–Mg–Si alloys produced by non-equilibrium processing methods: mechanical alloying and sputtering

Mechanical alloying (MA) and magnetron sputtering were used as processing techniques for the synthesis of various Ti–Mg–Si (Ti-rich) lightweight alloys. The samples were analysed by means of electron probe microanalysis (EPMA), X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). Results show that a supersaturated low range ordered solid solution of Ti(Mg, Si) was produced during milling of the Ti 75Mg 13Si 12 mixture, which crystallises at about 550 °C, giving rise to a dispersion of Ti 5Si 3 in a α-Ti matrix. A metastable (Ti, Mg) 5Si 3 intermetallic was observed to form during milling of the Ti 60Mg 10Si 30 sample obtained by two different milling processing routes: (i) from elemental Ti, Mg and Si powders and (ii) from titanium hydride (TiH 1.924), Mg and Si powders. The (Ti, Mg) 5Si 3 intermetallic decomposes into Ti 5Si 3 and Mg 2Si in the temperature range of 600–700 °C. Contrarily to the results obtained for the mechanically alloyed samples, no low range ordered or intermetallic phases were detected in the as-deposited sputtered thin films. All but the Ti 81Mg 6Si 13 thin film (lowest Mg content) contain two hcp phases, α-Ti and Mg, with [0 0 0 2] preferred orientations. The Ti 81Mg 6Si 13 thin film consists of an extended α-Ti solid solution. The heat treatment of the thin films lead to an increase of the structural order of these phases and to the formation of Ti 5Si 3.