Influence of Grit Blasting on the Roughness and the Bond Strength of Detonation Sprayed Coating
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. Sen, Naveen M. Chavan, D.S. Rao, and G. Sundararajan
(Submitted August 5, 2009; in revised form November 27, 2009) The process of roughening the surfaces by grit blasting prior to coating them using thermal spray techniques is very important to obtain consistently high tensile bond strength between the coating and the substrate. The available literature on the influence of grit-blasting parameters in the case of detonation spray or HVOF coatings is quite limited. The present study aims to study the influence of gritblasting pressure and alumina grit size on the roughening of the mild steel substrate, the resulting effect on the roughness of Cu, Al2O3, and WC-12Co coatings deposited by detonation spray coating and also on the tensile bond strengths of these coatings. Toward the above purpose, the velocity of the alumina grits have been experimentally measured using a high-speed imaging system and the tensile bond strength of the coatings have been experimentally obtained using the pin type test. The results from the above experiments point to the importance of not only the roughness of the grit-blasted mild steel substrate but also the roughness of the coatings subsequently deposited in determining the magnitude of the bond strength.
Keywords
alumina grit velocity, coating roughness, detonation spray coatings, grit blasting, substrate roughness, tensile bond strength of coatings
1. Introduction Thermal spray coatings, especially those obtained using high velocity oxy-fuel (HVOF) or detonation spray coating (DSC) techniques, are widely used to provide wear resistance to engineering structures and components operating in hostile environment. In the HVOF/DSC techniques, powder particles are heated to high temperatures and also accelerated to high velocities and then allowed to repeatedly impact the component surface to form thick coatings. A unique aspect of these HVOF/DSC coatings is that their adhesion/bonding with the substrate is largely mechanical in nature since the powder particles are invariably heated to temperatures well below their melting point. This is especially true in the case of cermet and ceramic coatings. To improve the coating-substrate adhesion, the component surfaces are always grit blasted to roughen them, prior to the coating process. Al2O3 is the most widely used grit material and commercial grit-blasting machines are readily available to grit blast and roughen even components with complex geometries. D. Sen, Naveen M. Chavan, D.S. Rao, and G. Sundararajan, International Advanced Research Centre for Powder Metallurgy and New Materials, Hyderabad, India. Contact e-mails: [email protected] and [email protected].
Journal of Thermal Spray Technology
A large number of process and other variables like the grit material and size, blasting pressure and time, stand-off distance, blasting angle and the hardness of the component/surface being grit blasted determine the magnitude and nature of roughening of the surface. Thus, to obtain a consistently high quality HVOF/DSC coating with a consiste
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