Oxidation behavior and interdiffusion of Ta-Al multilayer films and Inconel 617 alloy

Abstract

In this study, Ta-Al multilayer films were cosputtered on Inconel 617 through cyclical gradient concentration deposition. The oxidation behavior of the Ta-Al films and the interdiffusion between the Ta-Al films and Inconel 617 were evaluated through thermogravimetric analysis, X-ray diffraction, transmission electron microscopy, and Auger electron spectroscopy after the films were annealed in air at 400-800 degrees C. The results indicated that the Ta0.79Al0.21 multilayer films had a low O content even though O diffused inward through the entire film thickness after 8 h of annealing at 800 degrees C, which was attributed to the formation of an Al oxide scale due to the outward diffusion of Al in the initial oxidation stage. This under-stoichiometric Al2O3/Ta2O5 structure caused the produced films to exhibit a high hardness of 23.2 GPa and a high Young's modulus of 316 GPa. Moreover, the outward diffusion of Inconel 617 elements, namely Ni and Cr, was restricted by the oxidized films. However, the high Ta content in the Ta-Al films deteriorated the film adherence to the substrates due to a high volume ratio of Ta2O5/Ta. Furthermore, laminated Ta0.79Al0.21/Ta0.34Al0.66/Ti films were fabricated to improve the film-substrate adhesion. These films exhibited a high hardness of 17.1 GPa after annealing at 800 degrees C for 24 h.