Graphite-based solid lubricant for high-temperature lubrication
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ISSN 2223-7690 CN 10-1237/TH
RESEARCH ARTICLE
Graphite-based solid lubricant for high-temperature lubrication Wenjuan HUAI, Chenhui ZHANG*, Shizhu WEN State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China Received: 07 July 2020 / Revised: 08 September 2020 / Accepted: 23 September 2020
© The author(s) 2020. Abstract: High-temperature solid lubricants play a significant role in the hot metal forming process. However, preparing high-temperature solid lubricant is formidably challenging due to the stern working conditions. Here we successfully develop a new type of eco-friendly high-temperature graphite-based solid lubricant by using amorphous silica dioxide, aluminum dihydrogen phosphate, and solid lubricant graphite. The solid lubricating coating exhibits excellent tribological properties with a very low friction coefficient and good wear protection for workpiece at high temperature under the air atmosphere. An array of analytical techniques reveals the existence of solid lubricant graphite in the lubricating coating after the high-temperature friction test. A synergistic effect between the protective surface film and the solid lubricant graphite is proposed to account for such superior lubricating performance. This work highlights the synergistic effect between the protection layer and the lubricant graphite and further provides the insight in designing the high-temperature solid lubricant. Keywords: graphite-based solid lubricant coating; high temperature; air atmosphere; high lubricating performance
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Introduction
Metal forming is vital to manufacturing metals into various shapes for different applications. Among factors affecting the metal forming process, the friction between the metal and the mold plays a critical role. Friction determines the required force and, thereby, the energy needed to influence the intended changes of the shape through the bulk deformation of the workpiece. It also affects the stress and strain distribution and, hence, the quality of the final product. Generally, friction in metal forming processes is complicated as it depends on many variables. Among those variables, the lubricant is one of the critical parameters, which have been widely employed not only to reduce the friction and wear of workpiece and forming tools but also to promote the flow of metal and to aid the release of the finished parts [1–3]. During the hot metal
forming processes, however, conventional lubricants like oil-based lubricants do not work since they would burn when they reach the surface of the hot material. Therefore, solid-lubricating materials with a low friction coefficient and high wear resistance, as well as high efficiency and long durability over a relatively high temperature are required [4, 5]. High-temperature solid lubrication, although known for centuries, remains one of the formidable challenges encountered in the tribology field due to the difficulty in designing novel lubricating base materials [6, 7]. So far, graphite, molybdenum disulfide (MoS2), and polytetraf
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