Influence of substrate preparation on HVOF IN718 coating adhesion strength

Paper i proceeding, 2011

In the HVOF spray process, significant peening stresses are generated during the impact of semi molten particles on the substrate. Peening stresses contribute to the density of HVOF coatings, but no systematic study has been carried out to determine in which extent these stresses become beneficial or detrimental to the coating adhesion strength. Neutron Diffraction has been utilized in this work to evaluate the residual stress distribution through different peened surfaces. The investigation was performed on Inconel 718 HVOF coatings sprayed on Inconel 718 substrates for repair application. A Tensile Adhesion Test was developed to measure the resulting coating adhesion strength which normally exceeds the limitation of the standard ASTM-C633 glue test. Combined these experimental techniques yield a deeper understanding of residual stress formation in the HVOF process and thus a tool for process optimization. The relationship between developed stress state at the coating/substrate interface and stress state of the gritblasted substrate prior to spraying is given a particular interest.