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.