cohesion strenght test of selected commercial hvof coatings

High velocity oxy-fuel spraying (HVOF) being one of thermal spraying techniques, is deployed in many commercial applications mostly for very hard wear and/or corrosion resistant coatings. Supersonic speed of the spraying jet combined with temperatures around 5500 K is utilized to spray most metals, metallic alloys, cermets and superalloys [1-3]. Typical HVOF coatings are compact, dense, with very low porosity, low to moderate oxidation level and high bonding strength to substrate [1]. Cermets and superalloys are standardly commercially applied HVOF materials, demanded for superb wear resistance, high hardness, abrasion and erosion resistance and overall great performance in high stress and/or high temperature environments. Proper testing methods are required to evaluate quality of deposited coatings and consequently choose coating with optimized properties for demanded application. There are many testing methods standardly and widely used for evaluating properties of thermally sprayed coatings – such as superficial indentation, micro and nanoindentation on cross section of the coating, tensile adhesion strength test, many tribological tests, etc. [1]. This article concerns modified TCT (tubular coating tensile test) for testing cohesion strength of the coatings with the use of common tensile test equipment. In this paper, specimen assembly, coating deposition, testing procedure and calculation of results is described. Cohesion strengths of five HVOF commercial coatings: Stellite 6, Hastelloy C 276, Cr 3 C 2 -25NiCr, WC 10Co4Cr and NiCrFeSiBC are evaluated.