Since the strong internal order and mixed (metallic and covalent/ionic) bonding, intermetallic compounds often offer a compromise between ceramic and metallic properties when hardness and/or resistance to high temperatures is important enough to sacrifice some toughness and ease of processing. Recently, investigations of intermetallic matrix materials have been initiated, consequently leading to various novel high temperature solid-lubricating materials developments, such as nickel aluminum matrix, titanium aluminum matrix, ferric aluminum matrix, nickel silicon matrix and other high temperature solid-lubricating materials. Tribological properties of some intermetallic matrix solid-lubricating composites are displayed. Ni3Al-based intermetallic alloys may be an excellent matrix for high temperature solid-lubricating composite owing to its high temperature strength, good oxidation resistance and corrosion resistance behavior. Recently, a series of Ni3Al matrix high temperature solid-lubricating composites were developed. The solid-lubricating composites, which consist of Ni3Al matrix with solid lubricants (graphite, MoS2, hBN, Ag, Au, fluorides, inorganic salts etc.) and reinforcements(Cr, Mo, W, TiC, Al2O3, Cr2O3, Cr3C2, etc.), exhibit the low friction coefficient (μ<0.35) and wear rate (10−4∼10−6 mm3/Nm) at a wide temperature range from room temperature to 1000 °C. An optimized Ni3Al matrix high temperature solid-lubricating composite show satisfied mechanical and tribological properties. The extensive investigations provide the valuable guide to design high temperature solid-lubricating composite, as shown in the following conclusions. The effect of solid lubricants on the tribological behavior shows that the combination of Ag and fluorides exhibits optimal synergetic lubricating action, whereas the effects of reinforcements on tribological and mechanical properties represent that the metal alloying phases are superior to ceramic phases. The low friction coefficient at a broad temperature range is mainly attributed to the integrated factors. (1) Tribo-chemistry. At high temperature ambient, fluorides react with alloying elements to produce inorganic salts with high temperature lubricous properties. (2) Tribo-transfer. At various temperatures, the selected transfer films, which are the Ag-rich and fluoride-rich transfer film at low-moderate temperatures and the lubricating film containing inorganic salts at high temperatures, act a protective cover and reduce the direct contact of tribo-pair. (3) Triboglaze. At high temperatures, the glaze layer that is the complete and continuous oxide layer takes place on the worn surfaces, which is consisting of oxides and inorganic salts with lubricous properties. This glaze layer has both wear-resistant and friction-reduced functions. (4) The synergistic action. The lubricating properties at a broad temperature range are mainly attributed to the synergistic action of Ag, fluorides and inorganic salts, which develop the various lubricous films with testing temperature under the action of friction force, lubricant diffusion and tribo-chemical reaction. The NiAl matrix composites with addition of CuO has a favorable friction coefficient of about 0.2 and excellent wear resistance with the magnitude of 10−6 mm3/Nm at high temperatures (800 °C and 1000 °C), while the NiAleCreMoeCaF2eAg composite provides solid lubricating properties of 0.2–0.4 at a broad temperature range between room temperature and 1000 °C. When AgVO3 works as solid lubricant, the NiAleMoeAgVO3 and NiAleNbCeAgVO3 composites rubbing against Inconel 718 disk show satisfactory friction coefficient at 900 °C owing to the excellent lubricating effect of AgVO3 lubricants. As for other solid lubricants, the NiAle- Ti3SiC2eMoS2 composite offers more favorable friction coefficient of 0.12–0.29 from room temperature to 800 °C compared to NiAleTi3SiC2-WS2 composite and NiAlePbO composite. TiAl intermetallics have acted as structural materials owing to their advantages of low density, high specific strength and specific modulus. To improve the poor wear and friction properties, in recent years, TiAl matrix solid-lubricating composites are concerned widely and developed, such as TiAleAg composite, TiAleAgeTi3SiC2 composite, TiAlgraphene- Ti3SiC2 composite, TiAleAgeTiB2 composite,TiAleAgeBaF2/CaF2eTi3SiC2 composite, TiAleMoS2eTi3SiC2 composite, and so on. The results show that the TiAleAg composite has a relatively favorable friction coefficient of 0.25–0.21 and wear rate of 10−4 mm3/Nm from room temperature to 900 °C.Other intermetallic matrix high temperature solid-lubricating composites were also investigated. Fe3AleBa0.25Sr0.75SO4 solid-lubricating composites exhibits low friction coefficient of 0.19–0.29 and wear rate on the order of 10−5 mm3/Nm at 600–800 °C. The improvement of friction and wear properties at high temperatures can be attributed to the lubricating film of Ba0.25Sr0.75SO4 formed on the frictional surfaces.
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