Sustainable Direct Synthesis of TiAl Alloys Through Magnesiothermic Reduction

Direct synthesis of TiAl alloys through magnesiothermic reduction of an intermediate TiAl2O5 phase was demonstrated at various temperatures and Mg/TiAl2O5 molar ratios. X-ray diffraction (XRD) results verified TiAl alloys could be directly synthesized at a Mg/TiAl2O5 molar ratio of 25 at 900 °C. At lower Mg/TiAl2O5 molar ratios of 12.5 and 5, the desired TiAl alloys underwent a transition from the TiAl alloy to the TiAl2 alloy. Scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analysis indicated that a dense Al2O3 film could be easily generated on the surface of the TiAl alloy preventing further oxidation of TiAl alloys. The by-products from the magnesiothermic reduction mainly consisted of MgAl2O4 spinel, which could not be separated from the metallic alloys with a solution of diluted HCl and HNO3 but could be partially separated by particle size. Particle size screening suggested that particles larger than 45 μm mainly contained MgAl2O4 spinel-based by-products and particle size below 45 μm consisted of a mixture of TiAl2 alloys and MgAl2O4 spinel-based by-products.