The use of dense tungsten carbide cobalt coatings is wide spread in the oil and gas industry and particularly in the prevention of wear. However, their poor mechanical strength under harsh environmental conditions (including corrosion effects) can limit the coating functionality. In the present study, a metallurgical and mechanical/tribological investigation was performed on a composite mixture of three coating materials. These were Tungsten carbide cobalt (WC-12Co) of both, conventional micro sized Diamalloy 2004 and superfine InfralloyTM S7412 nanostructured WC-12Co, were blended with Diamalloy 1005 (Inconel-625: Nickel Chrome based alloy) to produce erosive/corrosive resistant coatings. These coatings were deposited by a HVOF thermal spray process onto carbon steel 4041 substrates typically used in oil/gas industry components. The metallurgical structure of the powders and coating surface morphology were investigated using SEM, EDS and XRD. The SEM and EDS results obtained show that coating mix P.S.4 (which contained 75% of nanostructured WC-12Co and 25% Diamalloy 1005) was the optimal coating microstructure amongst all of the blends. Its splats had a uniform cemented shape, supported by a highly dense coating microstructure with enhanced mechanical splat adhesion. Additionally, the fully melted particles within this mix provided lower viscosity of the matrix liquid phase and higher splat impact by the HVOF gun, resulting in high bonding strength at the interface with no presence of delamination occurring at the coating/substrate interface. Such microstructural properties benefit a components ability to protect itself from wear, and erosion-corrosion. The results of tensile, three point bending, fatigue, dry erosion wear, and erosion-corrosion again showed coating mix (P.S.4) to be the most superior coating amongst all of the blends. Additionally, the relationship between the various compositions of coating materials and the resulting coating mechanical properties were analysed through the development of process models using Statease Design Expert design of experiments (DOE). The result achievements demonstrated a reduction in maintenance cost and time experienced by the oil/gas industry; to eliminate shut-down cost for machines and the replacement of parts during operation. This HVOF coating (P.S.4) however could also suit many applications other than oil and gas based on the results found. However, P.S.4 would suit other in many engineering sectors subjected to erosion/corrosion.