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Effects of HVOF Parameters on Adhesion and Microstructure of Thermal Sprayed NiWCrBSi Coatings

Abstract This work evaluates the influence of processing parameters on the adhesion and morphology of a NiWCrBSi commercial alloy thermally sprayed using HVOF. A 33 factorial design experiment was used to establish the effects of the variables on coating quality. The equivalence fuel/oxygen ratio Fi, defined as the ratio [(F/O)working/(F/O)stoichiometric], was varied between 0·8 and 1·2, the spraying distance was varied between 380 and 570 mm, and the powder feedrate was varied between 60 and 120 g min-1. Response surface methodology was used to describe the empirical relationships among the parameters studied. The tensile bond strength was evaluated following ASTM C 633. Scanning electron microscopy, coupled with X-ray microanalysis, was employed to characterise the fractured surfaces after the test and to determine the fracture mode. The results indicated that the equivalence ratio Fi and the spraying distance were the main processing parameters which affected adhesion strength and the coating properties.