Temperature-dependent elastic properties of Ti1−xAlxN alloys

Ti1−xAlxN is a technologically important alloy that undergoes a process of high temperature age-hardening that is strongly influenced by its elastic properties. We have performed first principles calculations of the elastic constants and anisotropy using the newly developed symmetry imposed force constant temperature dependent effective potential method, that include lattice vibrations and therefore the effects of temperature, including thermal expansion and intrinsic anharmonicity. These are compared with in situ high temperature x-ray diffraction measurements of the lattice parameter. We show that anharmonic effects are crucial to the recovery of finite temperature elasticity. The effects of thermal expansion and intrinsic anharmonicity on the elastic constants are of the same order, and cannot be considered separately. Furthermore, the effect of thermal expansion on elastic constants is such that the volume change induced by zero point motion has a significant effect. For TiAlN, the elastic constants soften non-uniformly with temperature: C11 decreases substantially when the temperature increases for all compositions, resulting in an increased anisotropy. These findings suggest that an increased Al content and annealing at higher temperatures will result in a harder alloy. Funding agencies: Swedish Research Council (VR) [621-2011-4426, 621-2012-4401, 637-2013-7296]; Swedish Foundation for Strategic Research (SSF) [RMA08-0069, SRL10-0026]; VINNOVA [2013-02355(MC2)]; Erasmus Mundus Joint European Doctoral Program DocMASE; Ministry of EducationVid tidpunkten för disputation förelåg publikation som manuskript