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 Ti75Mg13Si12 mixture, which crystallises at about 550 °C, giving rise to a dispersion of Ti5Si3 in a α-Ti matrix. A metastable (Ti, Mg)5Si3 intermetallic was observed to form during milling of the Ti60Mg10Si30 sample obtained by two different milling processing routes: (i) from elemental Ti, Mg and Si powders and (ii) from titanium hydride (TiH1.924), Mg and Si powders. The (Ti, Mg)5Si3 intermetallic decomposes into Ti5Si3 and Mg2Si 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 Ti81Mg6Si13 thin film (lowest Mg content) contain two hcp phases, α-Ti and Mg, with [0 0 0 2] preferred orientations. The Ti81Mg6Si13 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 Ti5Si3.