Deposition and characterization of high velocity oxy-fuel sprayed nickel chrome boron silicium based coatings on stainless steel substrates

After plasma spraying, high-velocity-oxy-fuel (HVOF) spraying is fast emerging as the most versatile deposition technique for thermal sprayed protective coatings. In this context, the present work aims at the deposition of a class of inter-metallic/cermet coatings of nickel chrome boron silicium (NiCrBSi) and nickel chrome boron silicium+titanium diboride (TiB2) on 304 stainless steel substrates using high-velocity oxy-fuel spraying route. The cermet powder is prepared as the feedstock by mechanical mixing of the powders prior to spraying. Different coating samples are obtained by varying the flame-to-substrate spray distance (40 mm, 80 mm, 120 mm, 160 mm and 200 mm). These coatings are characterized in terms of their adhesion strength, deposition efficiency, thickness, and micro-hardness by conducting tests as per the ASTM standards. The surface and interface morphologies of the deposited coatings are studied using scanning electron microscopy. The possible phases present in the coatings, and the transformation of phases during deposition have been explored by x-ray diffraction analysis. It is found that the coatings exhibit fairly good interfacial adhesion, micro-hardness, and thickness values that varied significantly with the spray-distance. Further, the premixing of titanium diboride in nickel chrome boron silicium improved the mechanical and microstructural/compositional properties of the coatings.