With the rapid development of modern industry and other fields, higher requirements are put forward for antifriction materials working under high temperature, so that the problems of friction, wear and lubrication of materials under high temperature conditions are paid more and more attention [1,2] The corresponding high temperature self-lubricating material development and development. Metal-based solid self-lubricating materials produced by powder metallurgy have many unique advantages in terms of preparation process, structural composition, etc., and can produce materials with almost no segregation, uniform structure and good hot workability, especially in improving wear resistance The properties of the material are much better than those of traditional foundry materials . Such materials have broad application prospect under the special conditions of high temperature (including frictional heat generated by sliding friction). This article systematically discusses the development and progress of high temperature metal-based self-lubricating PMMA materials from different perspectives in order to provide reference for the design, preparation and development of high temperature self-lubricating materials with optimized combination of mechanical properties and friction and wear properties.
2 high temperature solid lubricant characteristics
For anti-friction materials that can work at higher temperature or higher temperature, high thermal strength, oxidation resistance and good anti-friction properties must be guaranteed. Only multi-component composite materials can meet these requirements . Powder metallurgy high temperature metal-based self-lubricating solid lubricant is a structural component added to the composite material, the addition of solid lubricant can improve the friction reducing properties of the material, but also affect the physical and mechanical properties performance. Depending on the nature of the lubricant, they can be added to the original mix in the form of a powder or added to the pores of the material after sintering. Depending on the method of addition, the lubricant can be added to the material matrix Interaction, partial or complete conversion into a new state. If the lubricant is added to the pores of the material that has been sintered, it does not change.
There are about 1000 kinds of solid lubricants , the lubricating mechanism is not the same, can be divided into three broad categories: (a) inorganic solid lubricant (1) soft metals, such as Pb, Ag, etc .; Metal compounds such as metal oxides PbO and Bi2O3, metal fluorides CaF2 and BaF2, metal sulfides MoS2 and WS2, metal nitrides BN and the like, metal selenides MoSe2 and WSe2, and the like; (3) Such as inorganic oxy acid salt, Zn3 (PO4) 2, etc .; (4) Others, such as graphite. (B) organic solid lubricants, such as PTFE; (C) composite solid lubricants, such as Mo-MoS2, Ag-PTFE-WSe2 and so on.
However, in which it can be mixed into the premix powder, after press-forming, to withstand the high sintering temperature without losing much of the lubricant.
Graphite, MoS2 is currently widely used as a solid lubricant, its friction coefficient and temperature relationship  As shown in Figure 1, graphite 540 ℃ in the atmosphere can be short-term use, long-term use at 426 ℃, while MoS2 at atmospheric pressure 399 ℃ can be short-term use, long-term use at 349 ℃, MoS2 showed excellent lubrication under high temperature and vacuum conditions. Graphite gradually loses its ability to lubricate in a dry atmosphere or in a vacuum. Adding MoS2 to the composition allows the material to work in a vacuum or dry gas above 400 ° C .
Figure 1 graphite and MoS2 friction coefficient --- temperature
When sulfur or sulfide is added to a composite, the properties of the material will depend on the nature and extent of its interaction with the matrix. Upon sintering, heating will be accompanied by the complete or partial decomposition of the sulphide, with the result that sulfur interacts with the metal framework of the matrix and therefore preventing changes in sulphide properties will greatly improve the final properties of the material. Wang et al. Prepared a Ni / MoS2 self-lubricating composite material with a MoS2 content of 80% by hot press sintering method and investigated the tribological properties at high temperature . It has been found [7,8] that some sulfides can improve the film-forming ability of MoS2 on metal substrates and inhibit the oxidation of MoS2. The performance of metal selenides and tellurides similar to the sulfide, in the vacuum and air friction coefficient and temperature relationship [4 \] as shown in Figure 2. Friction coefficient in vacuum than in the gas medium is low, their thermal stability, depending on the composition up to 400 ℃ 1350 ℃. Boron nitride (BN) has a layered hexagonal system, similar to graphite and MoS2, but has excellent thermal stability compared with graphite and MoS2, and exhibits a stable performance at about 900 ° C., showing good Lubrication performance.