Non-isothermal oxidation characteristic of titanium-aluminium intermetallic alloys
The non-isothermal oxidation behaviors of TiAl and Ti3Al alloys at 1450-1570 ℃ in a pure oxygen atmosphere were studied by using TGA/DSC simultaneous thermal analysis,SEM and EPMA characterizations and theoretical calculation.The results show that a continuous dense Al2O3 barrier layer is formed on the melt surface of TiAl alloy,when the oxidation temperature is higher than the melting point of TiAl alloy.The Gibbs free energy of Al reacting with O in the melt is 50-150 kJ∙mol-1 lower than that of Ti,Cr and Nb.The diffusion coefficient(D) of Al atom in the melt of TiAl alloy is about 1.7 times that of Ti atom.The Al atoms continue to diffuse to the melt surface and preferentially react with O to form a continuous and dense Al2O3 layer.The Al2O3 barrier layer effectively hinders the diffusion of oxygen and metal ions inside and outside the matrix.TiAl alloy melts and absorbs heat to reduce the matrix temperature and slows down the oxidation rate,resulting in the non-isothermal oxidation resistance of TiAl alloy is better than that of Ti3Al alloy in range of 1450-1570 ℃.
TiAl alloynon-isothermal oxidationoxidation mechanismoxidation kineticsignition
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