The Effect of Low Temperature Range Heat Treatment on the Residual Stress of Cold Gas Dynamic Sprayed Inconel 718 Coatings via Neutron Diffraction

Abstract

There has been considerable interest in the application of cold gas dynamic spray (CGDS) to deposit nickel-based superalloy coatings for the repair and development of high-value components that operate under extreme environmental conditions. The CGDS process introduces residual stresses in the coating layers, but inherently effects the subsurface of the substrate in a similar manner. The present study investigates the effect of low temperature range heat treatments (100-400 °C) on the residual stress of CGDS Inconel® 718 deposited onto a presolution-treated Al7075-T651 substrate. High spatial resolution nondestructive residual stress measurements were carried out via neutron diffraction on both the CGDS deposit and substrate. The low temperature range heat treatments displayed a significant effect on both the substrate and coatings. Residual stress relaxation was exhibited in coatings that were heat-treated at the lowest temperature, whereas an increased heat treatment temperature displayed an opposite effect, increasing both the compressive residual stress in the IN718 coating and the residual tensile stress in the substrate. It is proposed the difference in thermal expansion coefficient of the two materials was the main factor responsible for the residual stresses. The effect of post-heat treatment on coating microhardness and porosity is also presented.