Growth Kinetics of In Situ Fabricated Dense NbC Coatings on Gray Cast Iron
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JMEPEG DOI: 10.1007/s11665-016-2439-z
Growth Kinetics of In Situ Fabricated Dense NbC Coatings on Gray Cast Iron Liuliu Shen, Yunhua Xu, Nana Zhao, Ziyuan Zhao, Lisheng Zhong, Ke Song, Xiaolong Cai, and Juan Wang (Submitted June 12, 2016; in revised form September 20, 2016) In the present study, dense niobium carbide (NbC) coatings are fabricated by in situ techniques on gray cast iron (Fe) substrates at 1150 °C for 5 min, followed by a heat treatment at 990, 1010 and 1030 °C for 5, 10, 15 and 20 min. The microstructure, element composition and metallographic phase of the coating are characterized by scanning electron microscope, energy dispersive spectral and x-ray diffraction, respectively. Results show that the coating consists of NbC and a-Fe phases. NbC coating thickness ranges from 12.51 ± 1.4 to 29.17 ± 2.0 lm depending on the heat treatment temperature and time. In addition, the growth kinetics of dense niobium carbide coatings are estimated. A diffusion model based on FickÕs laws is used to explore the carbon diffusion coefficients of the dense NbC coating in the range of heat treatment temperatures in which the experimental results of the kinetics of the niobium carbide coating are in good agreement with those estimated using diffusion model. Keywords
dense niobium carbide coating, diffusion model, in situ, kinetics, macrostructure
1. Introduction Hard coatings of carbide and nitride of transition metal elements on the surface of gray cast iron are commonly used to improve the wear resistance of ferrous materials (Ref 1). During the past few years, the fabrication of ceramic coating has been considered as the most effective method to improve the wear and corrosion resistance of cutting tools and machine parts, especially for the purpose of prolonging the service life (Ref 2). Surface modification cannot only maintain the original matrix properties but also obtain the desired coating properties. There are many techniques of surface modification, such as thermoreactive deposition (TRD) (Ref 1, 3), chemical vapor deposition (Ref 4), laser treatment (Ref 5), physical vapor deposition (Ref 6), plasma jet cladding (Ref 7) and in situ synthesis (ISS) techniques (Ref 8). Although ideal results can be obtained by these methods, there still exist many problems such as limitation on coating thickness, high cost and complex equipment (Ref 9), largely limiting their practical applications in the field of coating fabrication. The recent in situ technique fabricated the coating which presents a series of excellent properties such as fine crystalline grain, excellent mechanical properties, and strong interfacial bonding of matrix with reinforced phase (Ref 10, 26). There are lots of interesting characteristics of Niobium carbide, especially for its apply to wear applications. Adding to, high toughness high hardness (Ref 11) and YoungÕs modulus of Liuliu Shen, Yunhua Xu, Nana Zhao, Ziyuan Zhao, Lisheng Zhong, Ke Song, and Xiaolong Cai, School of Materials Science and Engineering, XiÕan University of Technology, XiÕan 710048
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