Prediction of high temperature mechanical and thermodynamic properties of W-Mn alloys based on first principles method

Abstract

In this paper, four kinds of W-Mn alloy structure models are constructed, namely W15Mn1, W14Mn2, W12Mn4 and W8Mn8 alloys. By investigating the phonon spectra of these alloys, it is found that W8Mn8 alloy is thermodynamically unstable. Therefore, the mechanical and thermodynamic properties of W15Mn1, W14Mn2 and W12Mn4 alloys are calculated based on first principles method. Pure W is also introduced as a comparison object. The investigation demonstrates that the bulk modulus of W-Mn alloys decreases with increasing temperature. In particular, W14Mn2 and W12Mn4 alloys decay rapidly with the increase of temperature, which indicates that excessive doping of Mn in W leads to instability of W-Mn alloys at high temperatures. For W15Mn1 alloy, the coefficient of thermal expansion is greater than that of pure W, and increases with increasing temperature, showing reasonable thermal expansion behavior. For W14Mn2 and W12Mn4 alloys, the coefficient of thermal expansion increases rapidly with increasing temperature may lead to the deformation or destruction of W-Mn alloys at high temperatures. However, all alloys have lower thermal conductivity than pure W. The thermal conductivity follows the order: pure W˃W14Mn2˃ W15Mn1˃W12Mn4. At 0 K, doping Mn in W decreases the mechanical strength of pure W, but improves its ductility. Other parameters such as anisotropy, Debye temperature, melting point, hardness, free energy, entropy, heat capacity, and equilibrium volume are also investigated. The improvement of the above performance is more conducive to the application of W-Mn alloys in the aviation field and as plasma facing first wall materials in nuclear fusion.