The hydrogenation mechanism of PtAl and IrAl thermal barrier coatings from first-principles investigations

In addition to oxidation resistance, the improvement of hydrogen embrittlement is also a big challenge for the noble metal thermal barrier coating. Unfortunately, the hydrogenation mechanism of noble metal thermal barrier coating is unknown. In this study, we apply the first-principles calculations to investigate the hydrogenation mechanism of PtAl and IrAl thermal barrier coatings. In particular, we further study the influence of hydrogen on the mechanical and thermodynamic properties of PtAl and IrAl coatings. Two hydrogen occupied sites: H(1) and H(2) models are considered. In either case, hydrogen is stable in PtAl and IrAl coatings. It is found that hydrogen prefers to occupy the H(2) model, while the hydrogen in this model is surrounded by the two Pt atoms and four Al atoms. PtAl-H(1), IrAl-H(1) and IrAl-H(2) models not only weaken the volume deformation resistance, shear deformation resistance and elastic stiffness, but also reduce the Debye temperature of PtAl and IrAl coatings. However, the PtAl-H(2) model improves the shear deformation resistance and elastic stiffness, in addition to the improvement of Debye temperature of PtAl thermal barrier coating. The low mechanical properties are that the hydrogen weakens the localized hybridization between the noble metal and Al atom. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.