| Abstract: |
During thermal spraying the rapid solidification of droplets onto a substrate introduces significant mechanical constraints against shrinkage resulting in large magnitude tensile residual stresses in each splat. Some of these stresses are relieved through sliding, plastic deformation, microcracking (in ceramics) and debonding. Concurrent mechanisms of relieve of these stresses act to reduce the magnitude of them at different degrees. As a result, the amount of the stress generated during the formation of coating can become an indicator of the adhesion, cohesion, microcracking, yield strength, and plastic deformation (via impact of subsequent particles) of a deposited layer. In this paper, this principle is used to assess the adhesion of molybdenum plasma sprayed coatings deposited on steel substrates of different roughness. The residual stress is evaluated via in-situ curvature monitoring of single layer coatings. A direct correlation of higher tensile stresses with better adhered coatings on the rougher substrates was found. The results suggest that splats underwent sliding during quenching on smooth substrates resulting in reduced residual stress. A complementary characterization was carried out via SEM to account for disparities in DE, flattening ratios and continuity of the coatings.
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