Erosion Performance of HVOF-Sprayed Cr 3 C 2 -NiCr Coatings
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Gang-Chang Ji, Chang-Jiu Li, Yu-Yue Wang, and Wen-Ya Li (Submitted October 1, 2006; in revised form March 21, 2007) Cr3C2-NiCr coatings were deposited by high-velocity oxygen fuel (HVOF) spraying process under spray conditions of different flows of oxygen and propane gases, and spray distances. The orthogonal regression experimental design method was used for systematic investigation of the influence of spray parameters on the erosion performance of Cr3C2-NiCr coatings. Erosion tests were performed at different jet angles of abrasive particles. The erosion mechanism of Cr3C2-NiCr coatings was examined through the surface morphology and cross-sectional microstructure of the eroded coatings. The correlations of the carbide particle size and carbide content with the erosion rate were examined. It was found that the erosion occurred dominantly by spalling of splats from the lamellar interfaces. The spalling resulted from the propagation of cracks parallel to the interfaces between the lamellae exposed to the surface and underlying coating. The carbide particle size and content in the coating influenced significantly the erosion performance of Cr3C2-NiCr coatings.
Keywords
Cr3C2-NiCr coatings, erosion mechanisms, erosion performance, high-velocity oxygen fuel (HVOF)
1. Introduction Chromium carbide coatings are widely applied to the parts subjected to high-temperature wear and erosion (Ref 1-11). It is usually considered that the wear and erosion resistance of cermet coatings are predominatingly influenced by its microstructures including the splat size, carbide particle size, carbide content and carbide distribution within a splat, and the cohesion between the splats (Ref 11-14). On the other hand, the microstructure of high-velocity oxygen fuel (HVOF)-sprayed cermet coatings is significantly influenced by the microstructure of starting powder, spray system, and spray conditions (Ref 15-22). Previous studies suggested that the coatings with a higher amount of fine carbides embedded exhibit a better wear performance (Ref 13, 14). Recently, HVOF spray process is preferably used to deposit cermet coatings such as Cr3C2-NiCr, WC-Co, etc. This is because the coatings deposited by the HVOF process exhibit high density, low porosity, and excellent adhesive strength with much more carbide particles retained in the matrix of the cermet compared with plasma spraying process (Ref 15, 17). Gang-Chang Ji, School of Materials Science and Engineering, Jiujiang University, 551, Qianjin East Road, Jiujiang 332005, Jiangxi, China; Chang-Jiu Li and Yu-Yue Wang, State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, XiÕan Jiaotong University, XiÕan 710049, China; and Wen-Ya Li, Shaanxi Key Laboratory of Friction Welding Technologies, Northwestern Polytechnical University, XiÕan 710072, China. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
In HVOF process, however, the coating microstructure, which dominates the wear performance of the coatings, is significantly inf
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