High-Temperature Solid Lubricant Coating by Plasma Spraying Using Metal-Metal Clad Powders
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High-Temperature Solid Lubricant Coating by Plasma Spraying Using Metal-Metal Clad Powders Tiantian Zhang1,2 • Hao Lan1 • Shouquan Yu1 • Chuanbing Huang1 Lingzhong Du1 • Weigang Zhang1
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Submitted: 16 December 2016 / in revised form: 21 June 2017 / Published online: 5 July 2017 Ó ASM International 2017
Abstract NiCr/Ag-Mo composite coating was fabricated by atmospheric plasma spray technology using clad powders as the feedstock. Its tribological properties at variable temperature were evaluated using a ball-on-disk hightemperature tribometer in air. The results showed that compared with NiCr, the NiCr/Ag-Mo composite coating exhibited better lubrication effect and higher wear resistance at all test temperatures, especially above 600 °C. At 800 °C, NiCr/Ag-Mo composite coating showed the lowest friction coefficient of about 0.2 and its corresponding wear rate reached 2.5 9 10-5 mm3/Nm. Characterizations of NiCr/Ag-Mo composite coating revealed that at temperatures below 400 °C, Ag was smeared and spread onto the wear surface, reducing the friction and wear. At temperature above 500 °C, the Ag2MoO4 lubrication film formed by tribo-oxidation significantly improved the coating’s lubrication effect and wear resistance. Keywords atmospheric plasma spray clad powder silver molybdate solid lubricant coating
& Tiantian Zhang [email protected] Lingzhong Du [email protected] Weigang Zhang [email protected] 1
Laboratory of Particle Science and Engineering, State Key Laboratory of Multi-phase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, No. 1 Bei-er-jie, Zhong-guan-cun, Beijing 100190, People’s Republic of China
2
University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing 100049, People’s Republic of China
123
Introduction Solid lubricant coatings are widely applied in tribological contact parts working under extreme environments, such as high-temperature and high-vacuum conditions, where traditional liquid lubricants fail to provide effective lubrication (Ref 1-7). At temperatures above 400 °C, most conventional solid lubricants such as graphite and MoS2 lose their lubrication properties due to oxidation (Ref 8, 9). In order to reduce high-temperature friction and wear, many efforts have been made on various materials (Ref 1017). Recently, adaptive self-lubricating coatings have been considered promising materials for their good tribological properties over a wide range of temperatures. These coatings usually employ at least two components as solid lubricants to adjust the surface chemical compositions with the changes of temperature and reduce the friction. At present, one trend in developing adaptive self-lubricating coatings is focused on a Ag-Mo composite solid lubricant and on the study of its synergistic lubrication effect. Hu et al. (Ref 18) prepared a yttria-stabilized zirconia (YSZ) nanocomposite coatings by combining filtered vacuum arc, magnetron sputtering and pulsed laser deposition with addition of Ag and Mo as the solid lubricants.
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