Comparative study of mechanical properties and residual stress distributions of copper coatings obtained by different thermal spray processes

In this work, the influence of the thermal spraying processes, atmospheric plasma spraying (APS), high velocity oxygen fuel (HVOF), and vacuum plasma spraying ( VPS), on the microstructure and properties of copper coatings is discussed. The differences in microstructure, microhardness, and residual stress for each type of coating are shown. The X-ray diffraction (XRD) meth od is used to evaluate the mechanical anisotropical characteristics of the materials and the residual stress distribution. The particularity of this s tudy is that the thickness of the coating is of the millimetre scale; the m assive coating specimens without a substrate were obtained for XRD microela stic modulus measurements and for macrotensile measurement. Microhardness d istributions have been obtained in coatings and in substrates that pass thr ough the interface zones. It was observed that dense coatings could be obta ined by industrial processes such as APS and HVOF, but they induce oxidatio n in the copper coating. The copper oxidation is limited in the VPS process . The elastic modulus values measured by the in situ XRD method show that t he HVOF coating has more rigidity than the APS coating. HVOF and VPS copper coatings have higher microhardness values than the APS copper coating. The residual stress values are in traction in the APS, VPS, and HVOF coatings: the residual stress level in the HVOF and APS coatings is less important t han that in the YPS coating. The microstructure observations show that the VPS copper coating has a recrystallised structure whereas the APS and HVOF copper coatings have a splat type structure. As a consequence, the YPS copp er coating has a high Youngs modulus, an important mechanical resistance, a nd a high elongation as compared with the other copper coatings.