Preparing And Tribological Property Of High Temperature Self-lubricating Composites

Because of the oxidization above 450℃in air, common solid lubricant such as MoS₂ and graphite will lose lubrication action. With the development of modern industry, especially aviation industry and space technology, there are many parts and space devices working at critical condition, working regularly and lifespan of space devices depend on lubricating state. So research & develop new lubricates and its composites has much value in application and theory areas. It is one of the most important subjects in tribology field.Solid lubricants can be used in many routes, for examples, cover film fabricated by adhesives, additation added into oil and grease, composite prepared with several components. Lubricanting film's lifespan is very short, additationes will agglomerate, only composites can overcome these disadvantages, it also shows good lubricanting and mechanical properties. There are many uncertain elements about composite, such as the solution and matching of lubricants and matrixes; the grain size, distribution and concentration of lubricants; preparing methods.Firstly, we fabricated Ni-Cr based self-lubricanting composite by adding MoS₂ and LaF₃ into Ni-Cr alloy. The results show MoS₂ films generated on contact zone and conterface is the mechanism of antifriction at room temperature, but the oxide NiMoO₄ instead at high temperature.Oxide has good lubricanting property at high temperature. Liking MoS₂ and graphite, YBa₂Cu₃O₇ (YBCO) also has laminated structure, but its outstanding advantages are oxidation and wearing resistance. It also belongs to oxide ceramics, and its ceramic property such as frangibility needs to be improved. Doping is the one of the most simple and high efficient methods to improve frangibility of ceramics. At present, there are many reports on improving grain boundary weak-link, increase its critical current density (Jc) and mechanical properties with doping metals, instead of tribological properties. So paying attention to tribological properties can broad superconduct's application fields, it also has mach significance in developing new solid lubricats.We prepared YBCO powder by solid state reaction, XRD and SEM analysis indicate that the powderes are uniform, has little clutter phase. YBCO/Ag self-lubricating composite was fabricated by use of powder metallurgic method. Ag was doping in two routes, metal Ag powder and AgNO₃ crystal. This composite has more excellent superconductivity, mechanical properties and tribology properties. The triobology properties of composite were investigated on UMT-3 multi-function friction and wear tester from ambient temperature to high temperature in air. The results indicate: doping metal Ag can improve ceramic's frangibility effectively. Ag particles bed in matrix pores and act as connective phase. Ag particles also impede crack's initiation and expansion and bridge the cracks. When mass content of Ag is only 5%, composite has better tribology properties. On the effect of friction, Ag-film is the mechanism of antifriction, which generates on the contact zone of composite. Ceramic-matrix bears much loading. Soft metal film and hard matrix are the mechanism of tribology. The composite prepared from AgNO₃ crystal shows better overall properties.