Thermal spraying is often used to create coatings protecting parts against physico-chemical aggressions or improving superficial mechanical properties. It involves several problems because of the high temperatures of the process: cracks, porosity, coating adhesion. The authors use Vickers interfacial indentation test to characterize adhesive fracture between substrates and coatings. From the Lawn's relation two curves: load/crack length ratio (P/C3/2) vs crack length (C1/2) and ln P vs ln C are drawn for varying loads. They allow the determination of the type of residual stress, a coating fracture "toughness"/residual stress ratio (KC/[sigma]r) characterizing interfacial behavior and may lead, in some cases, to residual stress [sigma]r. Influence of superficial remelting by CO2 laser of cermet coating Cr3C2/Ni-Cr deposited on NiCrAlY covered steel and of annealing of Cr3C2/Ni-Cr coated cast iron are then studied. Possibility of reducing residual stress is shown at the same time as the interest of both approaches.
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Abstract