Microstructure and Properties of HVOF-Sprayed WC-(W,Cr) 2 C-Ni Coatings
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utz-Michael Berger, Sabine Saaro, Tobias Naumann, Michaela Kasˇparova, and Frantisˇek Zaha´lka (Submitted October 2, 2007; in revised form February 25, 2008) The composition WC-(W,Cr)2C-Ni is one of the standard compositions used for the preparation of thermally sprayed coatings by high velocity oxy-fuel (HVOF) spraying. Surprisingly, this composition has been poorly investigated in the past. Frequent use of commercial designations WC-ÔCrCÕ-Ni, WC-Cr3C2-Ni, and WC-NiCr indicates the insufficient knowledge about the phase compositions of these powders and coatings. The properties of these coatings differ significantly from those of WC-Co and WC-CoCr coatings. In this paper, the results of different series of experiments conducted on HVOFsprayed WC-(W,Cr)2C-Ni coatings are compiled and their specific benefits pointed out. The focus of this study is on the analysis of the microstructures and phase compositions of the feedstock powders and coatings. Unlike WC-Co and Cr3C2-NiCr, WC-(W,Cr)2C-Ni is not a simple binary hard phase—binder metal composite. The phase (W,Cr)2C with unknown physical and mechanical properties appears as a second hard phase, which is inhomogeneously distributed in the feedstock powders and coatings. As examples of coating properties, the oxidation resistance and dry sliding wear properties are compared with those of WC-10%Co-4%Cr coatings.
Keywords
dry sliding wear resistance, HVOF hardmetal coatings, oxidation resistance, WC-CoCr, WC-(W,Cr)2C-Ni
1. Introduction Feedstock powders and coatings made of the commercially available composition WC-(W,Cr)2C-Ni are based on an invention for which a patent application was filed in 1958 (Ref 1). As opposed to studies on WC-Co and WC-CoCr coatings, studies on these coatings are rarely found in the literature and most of them were performed in Japan. Okada and Yamada investigated the effect of an additional heat treatment on the coating properties (Ref 2). Ishikawa et al. (Ref 3-5) studied the influence of a gas shroud during HVOF-spraying on the microstructure, phase composition, corrosion, and wear properties of the coatings. Nakajima et al. investigated the rolling contact fatigue of HVOF-sprayed coatings (Ref 6-8). The composition was also selected in a number of comparative studies of different hardmetal coatings, e.g., by Toma et al. (Ref 9), Henke et al. (Ref 10), Cho et al. (Ref 11), and Kreye (Ref 12). The phase composition of the coating in the patent (Ref 1) is given as tungsten monocarbide (WC), a mixed carbide (WxCry)Cz, and nickel. In the comparative study Lutz-Michael Berger, Sabine Saaro and Tobias Naumann, Fraunhofer Institute for Material and Beam Technology (Fh-IWS), Dresden, Germany; and Michaela Kasˇparova and Frantisˇek Zaha´lka, Sˇkoda Vy´zkum s.r.o., Plzen, Czech Republic. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
published by Kreye (Ref 12), the phase composition WC-25(WCr)2C-5Ni is given. However, nowadays there are confusing designations used in the literature for this one and the same co
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