The mechanical and thermodynamic properties of Heusler compounds Ni2XAl (X = Sc, Ti, V) under pressure and temperature: A first-principles study

Abstract

The effect of pressure on structural and mechanical properties as well as the temperature dependence of thermodynamic properties, such as enthalpies of formation, elastic moduli, anisotropy, heat capacity and thermal expansion coefficient et al., of Ni2XAl (X=Sc, Ti, V) Heusler compounds are investigated implementing first-principles calculations. The influence of pressure on lattice parameters decreases as the increase of atomic number X (Sc, Ti, V). The Ni2XAl (X=Sc, Ti, V) show mechanically stable, ductility and anisotropy in 0–50GPa, and appropriate pressure can improve their mechanical properties because the bulk modulus B, shear modulus G, Young's modulus E, G/B and microhardness H almost linearly increase with pressure. The influence of pressure on B, G, E and H gradually decreases as the order of Ni2ScAl>Ni2TiAl>Ni2VAl, while it has an inverse effect on ductility and anisotropy. In addition, the resistance to volume deformation of NiAl alloys can be improved by second-phase strengthening with Ni2VAl and Ni2TiAl precipitates. Finally, the temperature and pressure dependences of bulk modulus, Debye temperature, heat capacity as well as thermal expansion coefficient of these compounds are elucidated using the quasi-harmonic Debye model. It is inverse for the effect of temperature and pressure on thermodynamic parameters.