The influence of vacancy on the mechanical properties of IrAl coating: First-principles calculations

The structural stability and mechanical properties of high-temperature materials are markedly influenced by the point defect. Although IrAl compound is a promising thermal barrier coating, the vacancy mechanism and relevant mechanical properties of IrAl are unclear. In this paper, we used the first-principles approach to study the vacancy mechanism and the influence of vacancies on the mechanical properties of IrAl. Three vacancies: Al vacancy (Al-va), Ir vacancy (Ir-va) and Ir-Al covacancy (Ir-Al-va) were considered in detail. We found that those vacancies are thermodynamically and dynamically stables. In particular, Ir-Al-va covacancy is more thermodynamically stable than that of monovacancy. Although those vacancies weakened the elastic stiffness, volume and shear deformation resistances of IrAl, they slightly improved its Vickers hardness. The calculated electronic structure indicated that the low elastic modulus of IrAl with those vacancies is attributed to the formation of IrIr and AlAl bonds.