Temperature-dependent elastic properties of Ti1−xAlxN alloys

Abstract

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.<p>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 Education</p><p>Vid tidpunkten för disputation förelåg publikation som manuskript</p

Finite-temperature elastic constants of paramagnetic materials within the disordered local moment picture fromab initiomolecular dynamics calculations

“…(2). Shulumba et al [18] showed that ∼80% of the temperature effect on the elastic constant of TiN could be captured with this method, at 20% of the computational cost. In this work, we extend the approach towards the magnetically disordered systems.…”

“…In disordered systems the symmetry of the crystal is broken. Therefore, we use a generalization of the TDEP method towards disordered systems, the so-called SIFC-TDEP [18]. Here it is applied to calculate vibrational properties at finite temperatures for magnetically disordered systems and to evaluate their elastic properties.…”

“…Thus, application of the proposed technique to study temperature-dependent elastic properties of CrN is justified. In addition, we investigate the possibility to enhance the efficiency of the simulations of elastic properties and present the results obtained from the recently developed method, symmetry imposed force constant temperature-dependent effective potential (SIFC-TDEP) [18], combined with the DLM picture, by relating the phonon properties of the magnetic disorder system and elasticity. Moreover, we compare both theoretical schemes with the results from more conventional calculations based on the Birch law in which the effect of temperature on the elastic moduli is introduced through the thermal expansion and discuss the accuracy of all the schemes considered in this study.…”

Theoretical Description of the Electron-Lattice Interaction in Molecular and Magnetic Crystals

“…It is worth to mention TDEP takes the full symmetry of the underlying crystal structure into account reducing the computational cost. TDEP, in its original format, works for ordered materials but it can be generalized to treat substitutionally disordered alloys [123].…”

Enhanced thermal stability and mechanical properties of nitrogen deficient titanium aluminum nitride (Ti0.54Al0.46Ny) thin films by tuning the applied negative bias voltage

“…2,4 The latter is based on a spinodal decomposition of the metastable cubic (c) solid solution c-(Ti,Al)N 5 into isostructurally coherent c-TiN and c-AlN rich domains at elevated temperatures. [6][7] The latter generate a hardness enhancement and hence improved mechanical properties of the c-(Ti,Al)N due to fluctuating strain fields 8 caused by coherency strains 9 and elastic stiffness differences [10][11] that obstructs dislocation motion. At even higher thermal loads, however, the c-AlN transform into its most stable phase, i.e.…”