| MAX phase materials combine the excellent properties of metal and ceramic.Such as good electrical conductivity and thermal conductivity,good mechanical processing properties of metal.High modulus,corrosion resistance and high temperature oxidation resistance of ceramic.It has low density,good thermal shock resistance and damage tolerance.The wide application prospects of MAX phase materials are due to those series of excellent performance.It can be used as structural material or coating material in extreme environment such as high temperature or high pressure,including nozzle valve of gas turbine engine,wing front of supersonic vehicle,high temperature heat exchanger.In this paper,the structure,elasticity and electronic properties of Ti2AlC,Ti3AlC2 and Ti5Al2C3 in Ti-Al-C ternary layered ceramics system were studied by first-principles method under high temperature.The structure,elastic and electronic properties of these materials were studied,and the effects of high pressure on their structures and properties were investigated.The results show that:?1?All crystals were structurally optimized under the pressure from 0 to 100 GPa to get their lattice constants.We also calculated the elastic properties,it is found that the elastic properties increase with pressure and they feat well with the experimental data.?2?Electronic properties and chemical bond properties were analyzed by electronic density of states,Mulliken analysis,and charge differential density.The results show that all three materials in Ti-Al-C ternary layered ceramics system have the comprehensive characteristics of metal bonds and covalent bonds.By compare with Ti2SiC and Ti3SiC2,we found that the bond strength of Ti-C is higher than Ti-A?A=Al,Si?bond.?3?We compare three crystals in the Ti-Al-C system and find out their correlation.We find that Ti5Al2C3 can be composed by Ti2AlC and Ti3AlC2,and the elastic properties is Ti3AlC2>Ti5Al2C3>Ti2AlC. |
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