•The SiC matrix solid-lubricating composites are prepared.•Synergism of Mo and CaF2 contributed to the lubrication of SiC at high temperature.•SiC matrix composites provided favorable lubricating properties at 800 and 1000 °C.•50 vol%SiC-20 vol%Mo-30 vol%CaF2 showed the best lubricating properties at 1000 °C.SiC matrix high temperature solid-lubricating composites with addition of different contents of CaF2 and Mo were fabricated by hot pressed sintering, and their tribological behavior was investigated over a broad temperature range between room temperature to 1000 °C. It was found SiC matrix composite with addition of 20 vol% Mo and 30 vol% CaF2 to exhibit excellent solid lubricity and wear resistance. Especially at 1000 °C, it has the lowest friction coefficient of 0.17 and a favorable wear rate of 4.08×10−6 mm3/N m. The low friction and wear mechanisms were discussed in detail.

•Tribological behavior of a Ni-based solid lubricant composite was studied.•The friction and wear tests are performed in air and vacuum from RT to 800 °C.•The high temperature tribological performance is distinct in air and vacuum.•The composite shows favorable self-lubricity in vacuum and air at RT-800 °C.•Oxidation leads to the difference of the friction behavior in air and vacuum.In aerospace, some moving parts will meet with simultaneous high temperature and vacuum environments. In this study, the tribological behavior of a nickel alloy matrix solid lubricant composite was contrastively investigated under both air and vacuum conditions from room temperature to 800 °C. Results showed that both the friction coefficient and the wear rate of the composite were highly dependent on testing temperature and atmosphere. The friction coefficient in vacuum was lower than that in ambient air. The compositions of the frictional surfaces were analyzed, based on which, the mechanism of friction and wear was proposed.

•Three nickel alloy matrix composites with Ag, CaF2 and MoS2 were prepared.•The tribological properties in air from RT to 700 ºC were investigated.•The COF and wear rate were dependent on the testing temperature.•Addition of Ag and MoS2 was the most effective to lubricant properties from RT-400 ºC.•The synergy of MoS2 and CaF2 showed the best self-lubricity from 400 °C to 700 ºC.There is an increasing need to high temperature solid lubricant materials and techniques for moving system worked at high temperatures. In this study, the nickel alloy matrix composites with solid lubricants of Ag, CaF2 and MoS2 were fabricated by hot pressed sintering approach and their tribological properties in air from room temperature to 700 ºC were investigated. Results indicated that the composites exhibited low friction coefficient of 0.16–0.40 and wear rate of (1–29.4)×10−5 mm3 N−1 m−1. The favorable lubricating properties were attributed to the synergistic effect of the added solid lubricants and the oxide formed in situ on the worn surface.

•Cu coated Ti3AlC2 particle was prepared by one-step electroless plating method.•AlCu/Ti3AlC2 composites were successfully fabricated by hot-pressing sintering process.•Cu layer could react with Al to form Al2Cu bridge interface between Ti3AlC2 and Al matrix.•Ti3AlC2 could play effective pinning role due to the enhanced Al2Cu interface.•AlCu/Ti3AlC2 composites showed significantly improved mechanical and tribological properties than AlTi3AlC2 composites.Al matrix composites reinforced with Ti3AlC2 and Cu coated Ti3AlC2 were prepared by hot-press sintering approach. It was confirmed that Ti3AlC2 displayed poor wettability with Al, resulting in the poor interfacial bonding strength between Ti3AlC2 and Al matrix. However, Al2Cu layer could be formed due to the reaction between Cu and Al during the sintering process, when Cu coated Ti3AlC2 was incorporated in Al matrix. Because of the formation of enhanced Al2Cu interface, the mechanical and tribological properties were significantly improved. The Al2Cu layer could bridge Ti3AlC2 particle and Al matrix effectively, which contributed to absorbing energy when load was applied, to provide better mechanical properties. Moreover, Ti3AlC2 particle could exhibit powerful pinning effect to inhibit two-body abrasion and adhesion wear, which was favorable for forming smooth tribo-oxidation surface to yield low friction coefficient. The wear mechanism was believed to be oxidation and fatigue wear.

•High temperature tribological behaviors of a Ni-based composite were studied.•The fluoride eutectic content inflicts significant effect on the wear behaviors.•The surface tribo-layer composition determines the tribological properties.This paper is aimed to characterize the new NiCrAlMo-12.5 wt. % Ag- X wt. % CaF2/BaF2 (X = 5 or 10) solid-lubricating composites, which have high strength and self-lubricity simultaneously from room temperature to 800 °C and thus would be a potential candidate for aerospace bearing applications. Additionally, clarification of the influence of fluoride content on the tribological responses of this material is another object. Sliding friction and wear performances of these composites as bearing materials are evaluated using a pin-on-rotating-flat disc configuration against an Inconel718 alloy pin. Also, the surface tribo-chemical reactions and mechanical properties of the composites are investigated and related to their tribological behaviors. Reducing the fluoride eutectic content leads to significant improvement on the wear resistance of the composites above 600 °C, which is strongly dependent on the surface tribo-chemical reactions and the interaction with the counterpart, not on the mechanical properties. The wear rate of the Inconel718 counterpart over the entire testing temperature range is as low as 10-7 mm3/(Nm).Download high-res image (346KB)Download full-size image

A high strength and wear-resistance nickel-aluminum bronze alloy was successfully prepared by hot-pressing sintering. The tribological performances of it sliding against AISI 52100 steel were studied in distilled water, seawater, divalent salt solutions and monovalent salt solutions. The effects of the main components of seawater on the tribological properties were first investigated. The results show that Cu–9Al–5Ni–4Fe–Mn alloy has a lower friction coefficient and wear rate in seawater and divalent salt solutions. The Cl− and SO42− adsorbed by the surface can accelerate corrosion and promote the formation of Cu2O, Al2O3, FeOOH and Fe2O3, which has an influence on the tribological performances. The distribution of CaCO3 and Mg(OH)2 on the surface also plays an important role in the reduction of the friction coefficient and wear rate. In addition, many substances transfer from the alloy to the steel surface and form a transfer layer during the friction process.

The controlled synthesis of large-scale nanocrystalline metals and alloys with predefined architecture is in general a big challenge, and making full use of these materials in applications still requires greatly effort. The combustion synthesis technique has been successfully extended to prepare large-scale nanocrystalline metals and alloys, especially iron alloy, such as FeC, FeNi, FeCu, FeSi, FeB, FeAl, FeSiAl, FeSiB, and the microstructure can be designed. In this issue, recent progress on the synthesis of nanocrystalline metals and alloys prepared by combustion synthesis technique are reviewed. Then, the mechanical and tribological properties of these materials with microstructure control are discussed.

•The wear resistance of nanocrystalline alloy improves more effective in vacuum.•The tribo-oxidation could mask the effect of hardness of alloys.•The adhesion and oxidation of nanocrystalline alloy have been restricted in vacuum.The tribological behavior of nanocrystalline Fe88Si12 alloy in vacuum environment has been investigated compared with coarse grained counterpart. The results demonstrated that the friction coefficient of the Fe88Si12 alloy reduced with the decrease of both grain size and oxygen partial pressure. The wear resistance of the Fe88Si12 alloy improved more effective in vacuum than in air as the grain size decreased. As the hardness and oxidation activity of the Fe88Si12 alloy decreased, the wear mechanism changed from adhesion and oxidation to plastic deformation and adhesion when the grain size and oxygen partial pressure decreased.

•Ni3Al alloy has the better anti-wear properties than Ti–6Al–4V alloy at dry friction and sea water conditions.•Ni3Al alloy in sea water circumstance has lower friction coefficient compared to that at dry friction condition.•Sea water has lubricating, cooling, and corrosive effects on the friction pairs.The tribological behavior of a Ni3Al alloy prepared by hot-pressed sintering was investigated at dry friction and sea water condition against AISI 52100 steel ball in ambient environment and at varying loads. The tribological results suggested that the Ni3Al alloy has the better wear resistance properties compared to Ti–6Al–4V alloy at dry friction and sea water conditions, and the Ni3Al alloy possesses the excellent wear resistance properties under sea water environment. Sea water plays a significant role in the improvement of tribological properties of the Ni3Al alloy, which has lubricating, cooling, and corrosive effects on the friction pairs.

•TiC improves obviously the wear-resistance of Fe–28Al–5Cr alloy at H2SO4 solution.•Wear rate of the composite with 50% TiC is 4–38 times lower than that of Fe–28Al–5Cr alloy.•The reasons for low friction coefficients are due to the formation of FeS and hydrated silica.•Wear resistance significantly increases with rising TiC amount.Sliding wear behaviour of Fe–28Al–5Cr and its composites containing 15, 25, 35 and 50 wt% TiC was investigated against a Si3N4 ceramic ball in 1 mol/L H2SO4 solution. The wear rate and friction coefficient were significantly reduced by the addition of TiC. The main reason should be the load carrying role of hard TiC and the formed FeS and hydrated silica films becoming more and more stable with TiC content. The dominant wear mechanism of the Fe–28Al–5Cr alloy and the 15% composite is ploughing and corrosive wear, but that of the 25%, 35% and 50% composites is corrosive wear.

The high-temperature tribological behaviour of Fe–28Al–5Cr alloy and its composites containing TiC was investigated against a Si3N4 ceramic from 25 to 800 °C. The high-temperature wear resistance of the materials was significantly improved by the addition of TiC, which was attributed to the high hardness of the composites, as well as the support role of hard TiC. The oxidation played an important role to friction and wear.Highlights► TiC improves wear-resistance of Fe–28Al–5Cr alloy at high temperature obviously. ► Wear rate of the composite with 50% TiC is 28–35 times lower than that of Fe–28Al–5Cr alloy. ► Enhanced wear-resistance of composites originates from high hardness and high strength. ► At 200–800 °C, the oxides play an important role in friction process. ► Wear resistance significantly increases with rising TiC amount.

A high-strength Fe85Ni15 alloy with lath martensitic structure was obtained by the self-propagating high-temperature synthesis technique. After tempering at 500 °C for 2 h, the hardness increased from 3.8 to 5.1 GPa, and the compression yield strength increased from about 1100 to 1500 MPa without much sacrifice of ductility. The strengthening effect might be attributed to the evolution of lath martensitic morphology and the reverse martensitic transformation.

The tribological properties of the nano-eutectic Fe1.87C0.13 alloy are investigated under dry-sliding against AISI52100 steel ball in ambient environment with varying applied load and sliding speed. As comparison, the tribological properties of the same alloy after annealing treatment, which is with coarse-grained microstructure, also are examined at the same testing condition. The worn surfaces of the alloys are analyzed by a scanning electron microscope (SEM). The wear resistance of the nano-eutectic Fe1.87C0.13 alloy is about 2–6 times higher than that of the annealed coarse-grained Fe1.87C0.13 alloy, and the wear rates increase with increasing applied load and sliding speed. Friction coefficients of the two alloys are almost same. These results demonstrate that the wear resistance of the Fe1.87C0.13 alloy is improved by forming nanostructure to obtain enhanced mechanical properties, but the friction coefficient is not significantly affected owing to almost the same friction surface states. The wear mechanism of the two alloys shows slight difference.

•The Ni-based composite exhibits excellent tribological properties at high temperature in a vacuum.•The lubrication lifetime and mechanisms of Ag and CaF2/BaF2 are clarified in vacuum.•Surface oxidation is detrimental to the wear-resistance of the composite.In this paper, the effect of the complex condition with high temperature and vacuum on the tribological properties of NiCrMoAl-Ag-CaF2/BaF2 solid-lubricating composite has been investigated. It presents that this composite displays the excellent tribological properties in vacuum than in air from room temperature to 800 °C. In vacuum, the friction coefficients are around or below 0.20 and superior to that in air. Besides, the wear rates in vacuum are at least one order of magnitude lower than those tested in air. They can be divided into three stages with the temperature (10− 7 mm3/Nm at room temperature and 200 °C, 10− 6 mm3/Nm between 400 and 600 °C, and 10− 5 mm3/Nm at 800 °C). Also, the surface oxidation behavior and the lubrication characteristics of solid lubricants (Ag and fluorides) in vacuum are clarified and related to the tribological properties.Download high-res image (269KB)Download full-size image

In this paper, the tribological behaviors of 20 and 40 vol% in situ TiB2 reinforced TiAl-based composites sliding against SiC balls were investigated in artificial sea water, and TiAl alloy was also studied as a comparison. The results showed that the TiAl-TiB2 composites are lubricated in artificial sea water and TiB2 is effective to improve the wear resistance of the TiAl alloy. Also, it was found that the tribological behaviors have a dependency on the applied loads and sliding speeds. Worn surface morphologies and composition together with electrochemical behaviors of the materials were evaluated and related to the tribological behaviors.