This paper presents the decision-making process used to simultaneously optimize the thickness and density of copper coatings produced by low-pressure cold spraying. Utility values based on both process parameters are analyzed for optimization using a Taguchi approach. The selected input parameters of powder feeding arrangement, substrate material, air stagnation pressure, air stagnation temperature, and standoff distance are shown to significantly improve the utility function of interest. The percentage contributions of the input parameters to optimize coating density and thickness are substrate material (50.03%), standoff distance (28.87%), air stagnation pressure (6.41%), powder feeding arrangement (4.68%), and air stagnation temperature (2.64%).

In this research work, an approach based on a Utility theory and Taguchi quality loss function (TQLF) has been applied to low-pressure cold spray (LPCS) process to deposit copper coatings, for simultaneous optimization of two potential response parameters i.e. coating thickness (CT) and surface roughness (SR). Utility values based upon these response parameters have been analyzed for optimization by using Taguchi approach. The selected input parameters of powder feeding arrangement, air stagnation pressure, air stagnation temperature and stand-off distance except substrate material, significantly improves the Utility function (raw data and S/N ratio) comprising of quality characteristics (coating thickness and surface roughness). The percentage contribution of the parameters to achieve a higher value of utility function is: stand-off distance (55.86%), air stagnation temperature (16.58%), air stagnation pressure (14.20%), powder feeding arrangement (5.12%) and substrate material (0.16%) respectively.

The present work evaluates the oxidation and hot corrosion resistance of high velocity oxy-fuel (HVOF) sprayed WC-NiCrFeSiB coating deposited on Ni-based superalloy (Superni 75) and Fe-based superalloy (Superfer 800H). The coated as well as uncoated specimens were exposed to air and molten salt (Na 2 SO 4 -25%NaCl) environment at 800 °C under cyclic conditions. The thermogravimetric technique was used to establish the kinetics of corrosion. The corrosion products were characterized using the combined techniques of X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe micro analyser (EPMA). The WC-NiCrFeSiB coating provides necessary resistance against oxidation and hot corrosion to both the nickel and iron based superalloys in the given environmental conditions at 800 °C. The oxides of active elements of the coatings, formed in the surface scale as well as at the boundaries of nickel and tungsten rich splats, have contributed for the oxidation and hot corrosion resistance of WC-NiCrFeSiB coatings, as these oxides act as barriers for the diffusion/penetration of the corrosive species through the coatings.

In this study, high velocity-oxy fuel (HVOF) technique was used to deposit Cr 3 C 2 -NiCr coating on the Ni-base superalloys for their hot corrosion applications. The coatings were characterised with regard to coating thickness, porosity, microhardness and microstructure. The hot corrosion behaviours of the bare and Cr 3 C 2 -NiCr coated superalloys were studied after exposure to molten salt (Na 2 SO 4 -60%V 2 O 5 ) at 900°C under cyclic conditions. Optical microscopy, XRD, SEM/EDAX and EPMA techniques were used to characterise the coatings. The thermogravimetric technique was used to establish kinetics of corrosion. The structure of the as sprayed Cr 3 C 2 -NiCr coating mainly consisted of γ-nickel solid solution with very low intensity peaks of Cr 7 C 3 and Cr 2 O 3 phases. Some porosity (less than 1.5%), inclusions, unmelted and semi-melted powder particles were observed in the structure of the coatings. Coating microhardness values were found to be in the range of 850-900 Hv (Vickers hardness). The Cr 3 C 2 - NiCr coating was resistant to hot corrosion in the given molten salt environment at 900°C. The hot corrosion resistance imparted by Cr 3 C 2 -NiCr coatings may be attributed to the formation of oxides of nickel, chromium, and spinels of nickel and chromium.