Mechanical Properties and Tribological Behavior of In Situ NbC/Fe Surface Composites
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JMEPEG DOI: 10.1007/s11665-016-2437-1
Mechanical Properties and Tribological Behavior of In Situ NbC/Fe Surface Composites Xiaolong Cai, Lisheng Zhong, and Yunhua Xu (Submitted May 31, 2016; in revised form November 10, 2016) The mechanical properties and tribological behavior of the niobium carbide (NbC)-reinforced gray cast iron surface composites prepared by in situ synthesis have been investigated. Composites are comprised of a thin compound layer and followed by a deep diffusion zone on the surface of gray cast iron. The graded distributions of the hardness and elastic modulus along the depth direction of the cross section of composites form in the ranges of 6.5-20.1 and 159.3-411.2 GPa, respectively. Meanwhile, dry wear tests for composites were implemented on pin-on-disk equipment at sliding speed of 14.7 3 1022 m/s and under 5 or 20 N, respectively. The result indicates that tribological performances of composites are considerably dependent on the volume fraction and the grain size of the NbC as well as the mechanical properties of the matrices in different areas. The surface compound layer presents the lowest coefficient of friction and wear rate, and exhibits the highest wear resistance, in comparison with diffusion zone and substrate. Furthermore, the worn morphologies observed reveal the dominant wear mechanism is abrasive wear feature in compound layer and diffusion zone. Keywords
friction and wear, in situ synthesis, microhardness, NbC-Fe composites
1. Introduction Metal matrix composites (MMCs) which consist of hard phases and a metal are often applied to engineering components. For instance, gray cast iron (GCI)-based composites are used for automobile industry, such as the disk brake system in which the wear resistance of surface is a main requirement (Ref 1-3). Scientific and technical efforts are always dedicated to developing wear-resistant surfaces without losing tenacity, in order to provide components that exhibit good behavior under special working conditions (Ref 4). However, tribological properties are considerably dependent on the microstructure of composites. The coefficient of friction (COF) and wear rate decrease with decreasing the particles size or increasing the volume fraction of the hard phases (Ref 5-7). Therefore, the preparation for wear-resistant surface composites, especially metal matrix reinforced by fine and hard carbide, nitride or boride particles, is an important topic in the tribological field. However, there is a variety of fabricating MMCs methods adapted for improving mechanical properties and wear resistance for composites (Ref 6-10). Among these methods, in situ synthesis (ISS) is one of the most promising processes because
Xiaolong Cai and Lisheng Zhong, School of Material Science and Engineering, XiÕan University of Technology, XiÕan 710048, PeopleÕs Republic of China; and Yunhua Xu, School of Material Science and Engineering, XiÕan University of Technology, XiÕan 710048, PeopleÕs Republic of China; and Shaanxi Key Laboratory of Nanomaterials and Nanotechnology,
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