Stress evolution in a Pt-diffused γ/γ′ bond coat after oxidation

The residual stresses in a Pt-diffused γ/γ′ bond coat after oxidation were investigated using the curvature and X-ray sin2ψ techniques. Contrary to the β-(Ni,Pt)Al, the Pt-diffused γ/ γ′ bond coat was in compression at room temperature due to a lower coefficient of thermal expansion. The stresses measured by the curvature method mainly came from the thermal misfit between the bond coat and the substrate, which decreased as the oxidation time increased. However, the stresses measured by the X-ray sin2ψ method exhibited an opposite trend. This discrepancy can be attributed to the different origins of the stress evaluated by different techniques. It demonstrated that the lattice misfit between the γ and γ′ phases exerted a significant influence on the micro-stress in the bond coat, and thus restricted the use of X-ray to measure the stress in the Pt-diffused γ/γ′ bond coat. In addition, the effect of stresses on the texture and rumpling behavior of the bond coat was also discussed.