Microstructural characterization and abrasive wear performance of HVOF sprayed Cr 3 C 2 –NiCr coating Gang-Chang Ji a, ⁎ , Chang-Jiu Li b , Yu-Yue Wang b , Wen-Ya Li b a Department of Materials Engineering, Jiujiang Polytechnical University, Jiujiang, Jiangxi 332005, PR China b State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, PR China Received 15 April 2005; accepted in revised form 7 October 2005 Available online 28 November 2005 Abstract Cr 3 C 2 –NiCr coatings were deposited by high velocity oxy-fuel (HVOF) process with different spray parameters to examine dominant microstructural factors in abrasive wear of the coatings. The microstructure of the HVOF sprayed Cr 3 C 2 –NiCr coatings was characterized by scanning electron microscopy and transmission electron microscopy (TEM). The apparent average size and volume fraction of carbide particles in the coatings were estimated through a quantitative imaging analysis. The formation of carbide phases in the coating was discussed based on the TEM observation results. The abrasive wear behavior of the coating was evaluated by the dry rubber wheel abrasive wear test and the wear mechanisms were elucidated. Influences of apparent size and volume fraction of carbide particles on the abrasive wear weight loss were examined through correlating the proposed relation with the experimental results. Results showed that Cr 3 C 2 particle size was significantly reduced after the spraying and Cr 7 C 3 carbide was present around Cr 3 C 2 particles, and Cr 23 C 6 carbide was dispersed in NiCr alloy matrix with a nano-crystalline structure. The three carbides were formed in the coating through different mechanisms. The removal of carbide particles in the coating was mainly responsible for the abrasive wear of the coating. The content and particle size of the Cr 3 C 2 carbides were the two key factors controlling the abrasive wear of the HVOF sprayed Cr 3 C 2 –NiCr coatings. © 2005 Elsevier B.V. All rights reserved. Keywords: High velocity oxy-fuel; Cr 3 C 2 –NiCr coating; Microstructure; Abrasive wear 1. Introduction Chromium carbide-based materials are generally employed to produce hard coating for elevated temperature wear application including sliding, fretting, abrasion, and erosion [1–11]. It is usually considered that the wear resistance of cermet coatings is predominately influenced by their micro- structures, e.g., carbide particle size, carbide content and carbide distribution within splats, and porosity, etc. [12–20]. Many investigations suggested that thermal sprayed dense cermet coatings with a higher amount of fine carbides embedded may possess a better wear performance [16,20]. Recently, high velocity oxygen fuel (HVOF) spray process has become a preferable process to deposit cermet coatings such as Cr 3 C 2 –NiCr and WC–Co. This is because the coatings deposited by the HVOF process exhibit high density, low porosity, excellent adhesive strength with much more carbide particles retained in the matrix compared with plasma spraying process [21,22]. In HVOF Cr 3 C 2 –NiCr coating, apart from Cr 3 C 2 carbide particles, the carbides Cr 7 C 3 and Cr 23 C 6 might be also present according to the reported results through X-ray diffraction analyses [23,24]. It is likely that these carbides are formed through decarburization of Cr 3 C 2 . However, as pointed out by Zimmermann and Kreye, the presence of Cr 7 C 3 and Cr 23 C 6 in the as-sprayed coating can not be proven solely by X-ray diffraction approach because their main diffraction peaks coincide with the lines referring to the NiCr and Cr 3 C 2 [25]. Moreover, as HVOF cermet coating is usually deposited in an ambient condition, the decarburization of Cr 3 C 2 seemed to be associated with oxidation of Cr 3 C 2 and heating of spray particles [25]. Previous work has also pointed out that the Surface & Coatings Technology 200 (2006) 6749 – 6757 www.elsevier.com/locate/surfcoat ⁎ Corresponding author. 551, Qianjin East Road Jiujiang, Jiangxi 332005, PR China. Tel.: +86 792 8312861; fax: +86 792 8312859. E-mail address: JGC@china.com.cn (G.-C. Ji). 0257-8972/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2005.10.005