The Structure,Mechanical And Thermodynamic Properties Of Ti-Al Alloys And Ti_nAC_n-1 Based On First-principle Study

Titanium aluminum alloy has many excellent properties so it is widely used in aviation,aerospace and other fields.TiAl alloy is a new kind of metal compound structure material,γ-Ti Al alloy has good properties such as low density,high specific strength,specific elastic modulus,good creep resistance and oxidation resistance,which can still maintain high enough strength and stiffness at high temperature.It is a very competitive material for aircraft and automobile engine.Secondly,MAX phase material also has the dual characteristics of metal and ceramics.In this paper,the first principle method is used to study the properties of Ti Al alloy,Ti₂AlC,Ti₂AlN,Ti₂GaC,Ti₂In C,Ti₃Al C₂,and Ti₃SiC₂,including lattice parameters,mechanical properties and thermodynamic properties with pressure ranges from 0 to 50GPa during the process,and the results are as follows:The calculated results including the elastic constants and modulus of elasticity at the pressure is 0 GPa are in good agreement with the experimental values and the theoretical values in the previous literatures,the materials doped by metal element can improve the cubic degree,so as to improve the ductility,the concentration has little influence on the Co element,the axial ratio is more than 1.it is beneficial to inhibiting the interaction of Ti-Al bonds and inhibit the material,so as to enhance the ductility of materials by doping Co element,and the concentration has a certain impact,the concentration is higher,the plasticity is better.It is found that with the increase of the pressure,the volume ratio of Ti₂AlX（X=C,N）decreases,and the effect of pressure on Ti₂AlC is greater than that of Ti₂AlN.The pressure can enhance the material’s ability to resist deformation,and with the increase of pressure,the deformation resistance is enhanced.The ductility of Ti₂Al N is better than that of Ti₂AlC.The brittle nature turns to ductile nature in 40-50 GPa for the Ti₂AlX since the value of B/G has exceeded the 1.75.Based on the calculation of thermodynamic properties,it is found that the bulk modulus decreases with the increase of temperature.But with the increase of pressure,the constant volume heat capacity C_V is the same as the constant pressure heat volume C_P change,and the C_V increases slowly at high temperature.The constant volume heat capacity C_V of Ti₂Al N following Dulong-Petit limit and it is higher than that of Ti₂AlN at high temperature.The influence of temperature and pressure on linear expansion coefficient mainly occurs at low temperature,and the influence of pressure on linear expansion coefficient is small when the pressure exceeds 30 GPa.With the increase of applied pressure,the compressibility of Ti₂InC is better than Ti₂GaC.It is found that the deformation resistance and ductility of Ti₂GaC and Ti₂InC increase with the increase of pressure,and when the pressure reaches 40-50 GPa,Ti₂GaC and Ti₂InC change from brittle material to ductile material.The ductility is improved.The Debye temperature has the same relationship with the bulk modulus and decreases with the increase of temperature,and the effect of pressure is opposite to the temperature.For heat capacity,the effect of pressure is lower than Ti₂GaC,and the heat capacity is higher Ti₂Ga C.Because of following Dulong-Petit limit,the heat capacity C_V is not rise.With the increase of pressure,the volume ratio of Ti₃AC₂（A=Al,Si）decreases,and the effect of pressure on Ti₃AlC₂ is greater than that of Ti₃SiC₂.The deformation resistance increases with the increase of applied pressure.The bulk modulus decreased with the increase of temperature,but increased with the increase of pressure.The relationship between constant volume heat capacity C_V and constant pressure heat capacity C_P was the same,and the C_V increased slowly at high temperature,and followed the Dulong-Petit limit of Ti₃AlC₂.The constant volumetric heat capacity C_V is higher than that of Ti₃SiC₂ at high temperature.The effect of temperature and pressure on the linear expansion coefficient mainly occurs at low temperature,and when the pressure exceeds 30 GPa,the pressure has little effect on the linear expansion coefficient.