How increasing cold spray coatings thickness affects their residual stress and properties

Abstract

Cold spray (CS) is a solid state deposition presented in the literature to produce coatings for various applications, e.g., corrosion-resistant 316L stainless steel, Ti light alloy parts repairing, and hydrophobic Cu coatings. CS sprays particles under high velocity, impacting onto a prepared surface or substrate, and the powders bond by a severe and fast plastic deformation, consolidating the coating layer by layer. The number of layers depends on the designed coating thickness since each powder and CS parameters results in a different layer thickness. This work evaluates three feedstock powders (Cu, Ti, and 316L) for CS processing, and the characteristics and properties of the CS-ed coatings, studying the effects of the thickness coatings on their microstructure, porosity, hardness, adhesion to the substrate, and residual stress generated. The images of microstructures were obtained by optical microscopy and SEM, and the near-to-surface residual stress was measured by X-ray diffraction (XRD). Increasing the coating thickness produced a substrate deformation due to the compressive residual stress dominating the coating, which is numerically obtained and proven by XRD. Besides that, increasing the coating thickness slight increased the deposition efficiency for Cu ant Ti, but went in the opposite way for 316L; reduced the coating adhesion to the substrate; and did not altered significantly the hardness