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(75)Mgl(3)Si(12) mixture, which crystallises at about 550(circle)C, giving rise to a dispersion of Ti5Si3 in a alpha-Ti matrix. A metastable (Ti, Mg)(5)Si-3 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)(5)Si-3 intermetallic decomposes into Ti5Si3 and Mg2Si in the temperature range of 600-700degreesC. 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-8l Mg6Si13 thin film (lowest Mg content) contain two hcp phases, alpha-Ti and Mg, with [0002] preferred orientations. The Ti81Mg6Si13 thin film consists of an extended alpha-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-5 Si-3 (C) 2003 Elsevier B.V. All rights reserved.