Influence of Process Parameter on Grit Blasting as a Pretreatment Process for Thermal Spraying
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K. Bobzin, M. O¨te, T.F. Linke, J. Sommer, and X. Liao (Submitted May 21, 2015; in revised form July 17, 2015) In thermal spraying, uncoated substrates usually require roughening. As the most common roughening method, grit blasting increases the surface area and produces undercuts in almost all cases, which facilitate mechanical interlocking and thus promote the bonding between the substrate and coating. The effects of grit blasting parameters, i.e., the particle size, the blasting angle, the stand-off distance, and the pressure, on the resulting surface topography are investigated. Furthermore, the efficiency and wear behavior of the blasting media are analyzed. Influences of three different blasting media, corundum, alumina zirconia, and steel shot, on the surface roughening, are compared. By varying adjusted blasting parameters, different initial conditions (surface topography) are created. Subsequently, the substrate is coated, and the coating bond strength is measured. One of the main results of this publication is that alumina zirconia and steel grit show a longer lifetime than pure alumina as a blasting media. Moreover, it has been shown that the blasting parameters such as grain size, working pressure, and history (wear status) of the abrasive particles have a significant effect on the resulting surface topography. Additionally, systematical analysis in this study shows that the blasting parameters such as stand-off distance and blasting angle have a small influence on the results of the blasting process. Another important conclusion of this study is that the conventional surface parameters that have been analyzed in this study did not turn out to be suitable for describing the relationship between the surface topography of the substrate and resulting bond strength.
Keywords
atmospheric plasma spray (APS), bond strength, grit blasting, roughness, substrate roughening
1. Introduction To be coated surfaces that require in almost all cases, an adequate pre-coating treatment is to ensure a successful coating application. Among all the treatment operations, such as cleaning, roughening, and masking, the roughening is possibly most critical to the coating adhesion, as the mechanical interlocking is one of the most important mechanisms for the bonding of thermal spray coatings. As one of the most used roughening methods, abrasive grit blasting is economically more attractive than other roughening methods (Ref 1). The result of the roughening depends on many factors, i.e., the size, density, and composition of the blasting media, as well as its impact velocity, angle of impingement, and the stand-off This article is an invited paper selected from presentations at the 2015 International Thermal Spray Conference, held May 11–14, 2015, in Long Beach, California, USA, and has been expanded from the original presentation. ¨ te, T.F. Linke, J. Sommer, and X. Liao, Surface K. Bobzin, M. O Engineering Institute, RWTH Aachen University, Aachen, Germany. Contact e-mail: [email protected].
Journal of Thermal Spray Te
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