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The effect of three principal, independent, high-velocity oxygen fuel (HVOF)-processing parameters on the properties of NiCoCrAlY coatings deposited using commercial powders is reported here. The design of experiments (DoE) technique at a two-level factorial and a central composite rotatable design was used to analyze and optimize the HVOF spraying process. The deposition parameters investigated were (1) fuel flow, (2) oxygen flow, and (3) stand-off distance. The effect of these processing variables was evaluated using selected responses, including porosity and oxide content, residual stresses, and deposition efficiency. Coatings with low porosity as well as with low residual stress were obtained using high fuel-rich conditions at a stand-off distance between 250 and 300 mm. At shorter and longer stand-off distances, respectively, either excessive flattening of splats or un-molten condition occurred, resulting in high levels of porosity and residual stress. The response surface, the empirical relationships among the variables, and the response parameters allowed the selection of optimum deposition parameters and the improvement of coating properties. [ABSTRACT FROM AUTHOR]

Measurement of mechanical properties in cermets is complex since they are formed by several phases. How to quantitatively determine the relationship between the performance and the complex microstructure of this particular group of materials, especially when analyzing the effect of the reinforcement phase, is still one of the top challenging problems yet to be solved. Hardness and elastic modulus of bimodal WC–Co HVOF thermal spray coatings doped with vanadium carbide (VC) additions were studied by performing a statistical analysis of nanoindentation results. A mathematical deconvolution procedure and a Weibull distribution analysis of hardness and elastic modulus results are proposed to identify the individual contribution of each phase to the mechanical properties of different WC–12Co coatings. Both analysis methods allowed to detect a reinforcing effect of vanadium on the hardness and elastic modulus of bimodal VC-doped coatings. The combination of VC additions and a bimodal WC particle size distribution in the WC–Co coatings proved successful in increasing their mechanical properties, as the coatings processed in this work showed better mechanical properties than that reported in the literature for coatings having exclusively a bimodal WC particle size distribution or those only doped with VC additions. [ABSTRACT FROM AUTHOR]