Xiyao Liu

To realize the adaptive regulation of friction performance for core mechanical components over a wide temperature range, an integrated antifriction and wear-resistant composite structure combining coating, texture, and lubricant was proposed and prepared. Arrayed circular micropore textures were fabricated on CSS-42 L high-temperature bearing steel with a nickel-based hard coating, and SnAg soft metal lubricant doped with the negative thermal expansion agent ZrW2O8 was filled into the textures. Cellular automaton models were established to simulate the diffusion process of the lubricant, and combined with systematic tribological experiments, the frictional behavior and adaptive regulatory mechanism at different temperatures were systematically analyzed. Simulation results based on cellular automata models show that with increasing temperature, the proportion of medium- and high-concentration regions of SnAg lubricant increases gradually and reaches 75.28% at 350 °C, confirming the favorable diffusion behavior at elevated temperatures. Tribological tests reveal that the 95Sn5Ag-filled coating and the 95Sn5Ag–10 wt% ZrW2O8-filled coating exhibit significantly superior tribological properties compared with the pure Ni-based coating across a wide temperature range. At 350 °C, the average friction coefficients of the 95Sn5Ag-filled coating and the 95Sn5Ag–10 wt% ZrW2O8-filled coating are 0.42 and 0.44, respectively, reduced by 35.4% and 39.7% compared with room temperature, and the wear rates decrease to 1.3×10−7 and 2.0×10−7 mm3·N−1·m−1. The lubricating layer thicknesses reach 4.48 and 4.18 μm, increasing by 164% and 80%, respectively. The 95Sn5Ag–10 wt% ZrW2O8-filled coating presents a more stable adaptive lubrication performance. The unique “inhibition at high temperatures and promotion at low temperatures” regulatory mechanism of ZrW2O8 effectively enhances the wide-temperature adaptability. The synergistic effect of coating, texture, and lubricant enables excellent antifriction and self-lubrication, which provides an efficient and feasible strategy for the active design and performance optimization of wear-resistant and lubricating functions of mechanical components.

The design of friction materials with integrated friction reduction and wear resistance functions has been a research challenge for many researchers and scholars, based on this problem, this paper proposes a nickel-based hard-soft composite coating structure. With 20CrMo steel as the matrix material, Ni20 powder doped with reinforced phase WC as hard coating material, using laser melting technology to prepare nickel-based hard coating on the surface of 20CrMo. PTFE emulsion and MoS₂ as a soft coating are prepared on the hard coating, and the nickel-based hard-soft composite coating is formed. At 6N-0.3 m/s, the new interface structure obtains the optimum tribological performance, and compared to 20CrMo, the friction coefficient and wear amount are reduced by 83% and 93% respectively. The new friction interface can obtain stable and prominent tribological properties at wide load and low to high speed, which can provide the guidance on the structural design of friction reduction and wear resistance materials.

As a high-temperature structural material, Ni₃Al matrix composites are often used to manufacture basic mechanical components that need to be used in high-temperature conditions. To meet the increasing demand for metal matrix composites with an excellent tribological performance over a wide temperature range, Ni₃Al matrix self-lubricating composites containing Sn-Ag-Cu and Ti₃SiC₂ (NST) were synthesized via laser-melting deposition. Dry sliding friction tests of NST against Si₃N₄ ball were undertaken from 20 to 800 °C to investigate the tribological behavior and wear-triggered self-healing properties. The results show that the tribological behaviors of NST are strongly dependent on the testing temperature and self-healing properties. At low and moderate temperatures from 20 to 400 °C, as the Sn-Ag-Cu flows into the cracks and is oxidized during sliding friction, while the cracks on the worn surface are filled with oxides consisting mainly of Al₂O₃, SnO₂ and CuO. At higher temperatures of 600 and 800 °C, the cracks are filled by the principal oxides of Al₂O₃, TiO₂ and SiO₂ due to the partial decomposition and oxidation of Ti₃SiC₂. Compared with other testing temperatures, the recovery ratio relative to the Ni₃Al base alloy of the cracks on the worn surface of NST is the highest at 400 °C, which is about 76.4%. The synergistic action mechanisms of Sn-Ag-Cu and Ti₃SiC₂ on the crack self-healing from 20 to 800 °C play a significant role in forming a stable solid lubricating film, improving the anti-friction and wear resistance of NST. The results provide a solution allowing for metal matrix composites to achieve excellent lubrication stability over a wide temperature range by virtue of the crack self-healing properties.

Improving the tribological performance of M50 steel under the conditions of wide load range is of great significance. In this study, the interfacial structure of surface micropores filled with Sn–Ag–Cu or Sn–Ag–Cu/whisker carbon nanotubes (whiskerCNT) of M50 material was prepared by laser additive manufacturing and high-temperature infiltration. From 2 to 22 N, the lubrication characteristics of Sn–Ag–Cu and whiskerCNT in surface micropores of M50 was investigated. Results indicate that Sn–Ag–Cu can precipitate to the worn surface and form a lubricating layer, which has a good lubricating effect. Moreover, the flow behavior of Sn–Ag–Cu on a worn surface can play the role of crack healing. At higher load, the strength of the lubricating film is enhanced by whiskerCNT, which renders the lubricating film not vulnerable to premature rupture.

In order to investigate the effect of synthesis methods on tribological behaviors of M50 matrix self-lubricating composites, M50-5wt.%Ag-10wt.%Ti3SiC2 self-lubricating composites (MAT) are prepared by spark plasma sintering (SPS) (MATS) and selective laser melting (SLM) (MATM) respectively. For comparison purposes, M50 steel samples are prepared by SPS (MS) and SLM (MM). The dry tribological behaviors of MS, MM, MATS and MATM against Si3N4 ceramic balls are investigated at 0.2 m/s-15 N from 25 to 450 oC. The results show that Ag, Ti3SiC2, TiC and Ti-Si-oxides can improve the tribological performance of MAT. The anti-friction and wear-resistant performance of MATM is better than that of MATS due to the fine structure of MATM.