Effect of Powder Characteristics on Properties of Warm-Sprayed WC-Co Coatings
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Pornthep Chivavibul, Makoto Watanabe, Seiji Kuroda, Jin Kawakita, Masayuki Komatsu, Kazuto Sato, and Junya Kitamura (Submitted April 24, 2009; in revised form October 2, 2009) In high-velocity oxy-fuel (HVOF) spraying of WC-Co coatings, the decomposition and decarburization of WC during deposition are responsible for their much lower toughness compared with a sintered bulk WC-Co. In a previous study, Warm Spray (WS) process, which is capable to control the flame temperature used to propel powder particles, was successfully applied in an attempt to suppress such detrimental reactions by keeping particlesÕ temperature lower than their melting point. The coatings deposited by WS process showed no or little formation of W2C and g phases and demonstrated moderately improved fracture properties. However, there is still a gap in fracture toughness between WS coatings and the corresponding sintered bulk. In order to optimize the properties of the WS coatings, the effect of original powder sizes were investigated. Microstructural characterization and phase analysis were carried out on deposited coatings by SEM and XRD. The results show that the feedstock powder size has substantial effects on the properties of the coatings, i.e., the smaller powder showed improved properties.
Keywords
coating, HVOF, powder size, warm spray, WC-Co
1. Introduction WC-Co cermet coatings have been used to enhance the wear resistance of various engineering components in a variety of industrial environments. Many thermal spraying techniques such as air plasma spraying (APS) and highvelocity oxy-fuel (HVOF) spraying can be applied to deposit WC-Co coatings, however, the properties of such coatings strongly depend on the spraying technique. Compared to other spraying techniques, HVOF spraying is one of the best methods for depositing conventional WC-Co cermets, because the higher velocities and lower
This article is an invited paper selected from presentations at the 2009 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Expanding Thermal Spray Performance to New Markets and Applications: Proceedings of the 2009 International Thermal Spray Conference, Las Vegas, Nevada, USA, May 4-7, 2009, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2009. Pornthep Chivavibul, Makoto Watanabe, Seiji Kuroda, Jin Kawakita, and Masayuki Komatsu, Composites and Coatings Center, National Institute for Materials Science, Ibaraki, Japan; and Kazuto Sato and Junya Kitamura, Fujimi Incorporated, Gifu, Japan. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
temperatures experienced by the powder result in less decomposition of WC during spraying process (Ref 1). Therefore, coatings with higher amount of retained WC and lower porosity are expected. However, when compared to sintered WC-Co, which has been fabricated in carefully controlled sintering condition,
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