Anisotropic Elasticity of APS and HVOF CoNiCrAlY Coatings Studied by Resonant Ultrasound Spectroscopy with Laser Doppler Interferometry

• Published in: Journal of thermal spray technology Vol. 28; no. 5; pp. 1017 - 1024
• Main Authors: Adachi, Kanta, Waki, Hiroyuki
• Format: Journal Article
• Language: English
• Published: New York Springer US 15.06.2019
• Subjects: Analytical Chemistry; Characterization and Evaluation of Materials; Chemistry and Materials Science; Corrosion and Coatings; Machines; Manufacturing; Materials Science; Peer Reviewed; Processes; Surfaces and Interfaces; Thin Films; Tribology; Young’s modulus; anisotropic elasticity; MCrAlY; thermal spray coating; resonant ultrasound spectroscopy; mechanical properties
• ISSN: 1059-9630; 1544-1016
• DOI: 10.1007/s11666-019-00878-w

The splat-based layered structure of thermal spray coatings leads to elastic anisotropy; however, elucidating the anisotropic elastic properties of such coatings is a challenging subject because of the limited sample size and microstructural factors such as high defect level. The objective of this study is to investigate the anisotropic elasticity of the as-sprayed and heat-treated CoNiCrAlY coatings prepared by atmospheric plasma spraying (APS) and high-velocity oxygen fuel (HVOF) spraying. For this purpose, we measure all five elastic constants accurately using resonant ultrasound spectroscopy with laser Doppler interferometry. This approach realizes the correct mode identification of the measured resonance frequencies, even for coatings with high internal friction by comparing the measured and calculated displacement distributions, providing a precise determination of the elastic constants with inverse calculation. We determined that an oriented array of defects causes a significantly low Young’s modulus along the spraying direction in both the as-sprayed coatings. Our measurements on the heat-treated coatings revealed that thermal treatment makes the APS coating stiffer than the HVOF coating, whereas the stiffness anisotropy of the APS coating remains stronger compared to the HVOF coating, even after heating. This phenomenon is consistently explained by focusing on the oxides in the coatings.