Abstract
Mechanical characterization of plasma-sprayed coatings at microscopic level represents a major challenge due to the presence of numerous inherent microstructural features such as cracks, pores, or splat boundaries, which complicate coatings characterization by conventional testing methods. Need for reliable testing of structural integrity of newly developed multiphase plasma-sprayed coatings introduced even more complexity to the testing. In this study, applicability of indirect vibratory cavitation test (adapted from ASTM G32 standard) for such testing was evaluated. Three plasmasprayed coatings having distinctive microstructures were tested: i) conventional alumina coating deposited from coarse powder, ii) hybrid coating deposited by co-spraying of coarse alumina powder and fine yttria-stabilized zirconia (YSZ) suspension, and iii) compact alumina coating deposited from fine ethanol-based suspension. Differences in the coatings internal cohesion were reflected in different failure mechanisms observed within the cavitation crater by scanning electron microscopy and mean erosion rates being i) 280 μm/hour, ii) 97 μm/hour and iii) 14 μm/hour, respectively.
Highlights
Plasma-sprayed coatings belong to the family of thermal sprayed materials and are used in numerous applications, typically to protect the substrate material from the aggressive environments
Thermal barrier coatings or wear-resistant coatings may be listed as typical examples
It is desirable to seek for new types of tests which may be applied for plasma-sprayed coatings and provide measure of the coatings durability reflecting internal coating cohesion and/or adhesion to the substrate
Summary
Plasma-sprayed coatings belong to the family of thermal sprayed materials and are used in numerous applications, typically to protect the substrate material from the aggressive environments. It is desirable to seek for new types of tests which may be applied for plasma-sprayed coatings and provide measure of the coatings durability (integrity) reflecting internal coating cohesion and/or adhesion to the substrate. Such test should be highly repeatable, representative for the whole coating, economical, and easy to perform on samples with simple geometry with coatings having as-sprayed as well as finished surface. For testing of plasma-sprayed coatings, it is interesting that individual cavitation bubbles erode the tested coating at microscopic scale (reflecting the coatings microstructure), but at the same time, their number is high enough to provide representative coatings characteristics. Test was applied on three ceramic coatings which were expected to have greatly different resistance against cavitation
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