Theoretical Study Of X(Hf,Ta,W,Re) Alloying Effect On Mechanical And Thermodynamic Properties Of ?-TiAl

As an ideal high-temperature structural material,y-TiAl is widely applied in aerospace,automobile and other related industries,due to its low density,high specific strength as well as good creep and oxidation resistance.Alloying elements addition is an effective way of improving the performance of alloy.Hf,Ta,W and Re alloying has been investigated extensively to improve the mechanical properties of y-TiAl,but the study on thermodynamic properties is still absent.In this work,density functional theory(DFT)and quasi-harmonic approximation methods were applied to calculate the electronic structures and the thermodynamic functions of Ti16Al16,Ti15Al16X and Ti16Al15X(X=Hf,Ta,W,Re),in order to investigate the effective alloying method to improve the ductility and resolve the contradiction of the thermal stability and hot strength of TiAl.The calculated results indicating that the structure of X(X=Hf,Ta,W,Re)alloying are stable.The energy difference of Ti15Al16X and Ti16Al15X suggest that Hf and Ta tend to occupy Ti-site,W and Re tend to replace Al atom.The axial ratios show that Hf,Ta,W,Re occupy the Al-site and Hf occupy Ti-site can improve the ductility of TiAl,and Ta,W,Re occupy Ti-site has little influence on the ductility.Through the charge density it is noted that Hf doping weakens the bonding strength,make the TiAl alloy become soft.While Ta,W,Re strengthen the bonding strength,enhance the compression resistance and the strength of alloy.X atoms doping make the transverse acoustic branch disappear in Ti16Al16,it reveals that X atoms have obvious effect on the transverse acoustic branch.Acoustic branch is closely related to the thermodynamic properties of materials,it is obvious that the alloying atoms have significant effect on the thermodynamic properties of the alloy.The calculated results showed that Ta,W,Re substituting Ti atom can increase the hot strength and thermal stability of alloy simultaneously.Ta,W,Re substituting Al show the high hot strength in the temperature range of T<520 K,T<650 K,and T<750 K,respectively.With the increase of temperature,they exist thermal stability deficiency.Ti-Al-Hf has not a better effect on TiAl in the whole temperature range.