Residual Stress Measurement in a Pt-Aluminide Bond Coat

The residual stress induced in a Pt-aluminide bond coat formed on a single-crystal superalloy has been measured. The stresses arise because of the thermal expansion misfit with the substrate on cooling from the manufacturing temperature. Since the lattice parameters are unknown, the interpretation of diffraction measurements is problematic, and the “wafer” curvature method has been applied. This method required that the substrate thickness be systematically reduced by mechanical thinning. It was also required that curvature measurements be made with the bond coat present as well as after it had been removed by thinning. This approach revealed that the bond coat is in residual tension, 140MPa, consistent with its thermal expansion coefficient, relative to that for the substrate.