Theoretical Study On The Stability And Oxidation Resistance On Surface Of Titanium-Aluminium Intermetallic Compound

Titanium-aluminium based alloy is an alloy which is based on titanium-aluminium intermetallic compound. It becomes to a promising candidates of high temperature structural materials in aeronautics and astronautics, because of its properties of low density, high specific strength and oxidation resistance etc. However, their ductibility and oxidation resistance need to be improved further. Therefore, it has important theoretical significance and potential applied value for the theoretical study on titanium-aluminium intermetallic compounds and their oxide films.Firstly, basing on Materials Studio and its modules of Visualizer and CASTEP, we have performed geometry optimization and calculation of free energy for crystal structure of titanium-aluminium intermetallic compound. The results of geometry optimization for Ti₃Al, TiAl and TiAl₃ by GGA-RPBE, GGA-PBE, GGA-PW91 and LDA-CA-PZ show good agreement with lattice parameters measurements from experiments. GGA-RPBE's are nearest. The lattice parameters of three crystal structures are a=b=5.77, c=4.67; a=b=3.99, c=4.03 and a=b=3.80, c=8.52. And a are bigger than experimental data 0.17%, 0.00%and -1.30%respectively, c are bigger 1.30%, -0.98%and -0.70%respectively. Free energies of new crystal structures of Ti₃Al, TiAl and TiAl₃ with results of GGA-RPBE have been calculated by these four methods. The results show that, free energy calculated by three GGA methods is near to each other and less than zero. But the result calculated by LDA is higher than them. All these show the stability of three crystal structures of Ti3Al, TiAl and TiAl3. Secondly, we calculate the free energies of some common metals and their oxides in industry. Considered thermodynamics and space structure,α-Al₂O₃ is one of the best choice for oxidation resistance. Basing on the probability wave theory of atomic configuration, we obtained seven ordered structures by analyzing and designning oxidation resistance film ofα-(Al_xCr_2-x)O₃. It presents knowledges for the study of high temperature oxidation resistance in future.