Metastable orthorhombic phases at ambient pressure in mechanically milled pure Ti and Ti–Mg

Nanocrystalline Ti and Ti–20 at.% Mg produced by mechanical milling were characterized using nanobeam diffraction. Metastable ω (hexagonal) and γ (orthorhombic) phases were observed in the pure Ti, while γ, a new orthorhombic ε phase and a face-centred cubic (fcc) phase were identified in the Ti–Mg. γ, found so far only at high pressures, was produced by a combination of high impact pressure and shear stress during milling. The forced dissolution of Mg caused the formation of the ε and fcc phases.