Zengshi Xu

Sliding Speed and Load Dependence of Tribological Properties of Ti3SiC2/TiAl Composite

The tribological properties of Ti3SiC2/TiAl composite (TTC) slid against a GCr15 steel counterface were investigated at sliding speeds in the range of 0.2–0.8 ms−1 and loads that ranged from 2 to 8 N. The results showed that the tribological properties of TTC strongly depended on the covering percentage of tribofilm on the TTC worn surface, which varied with changes in sliding speed and load. The tribofilm mainly consisted of Al-Ti-Si oxides, which provided a self-antifriction action that resulted in a reduction in the friction coefficient and an increase in the wear rate.

Effect of graphene nanoplate addition on the tribological performance of Ni3Al matrix composites

The main objective of this work has been the characterization of wear behavior of the graphene nanoplates (GNPs) in Ni3Al matrix composites (NMC). The friction and wear behaviors of NMC with the addition of 1 wt.% GNPs against Si3N4 ball are tested under different loads using a constant speed of 0.2 m/s. Tribological test results have revealed that small amounts of GNPs are able to drastically improve the antifriction and antiwear properties of NMC. A possible explanation for these results is that, the GNPs not only provide an enhanced effect for NMC to produce better wear resistance, but also form a local protective layer on the contact surfaces to reduce the friction. The investigation shows that GNPs hold great potential applications as an effective solid lubricant for Ni3Al matrix composites and possibly other alloys.

Tribological Behavior of NiAl–1.5 wt% Graphene Composite Under Different Velocities

The progress in aerospace field requires a new NiAl matrix composite that can stand against wear and decrease the energy dissipation through decreasing friction. In this study, the tribological behavior of NiAl–1.5 wt% graphene composite is investigated at room temperature under a constant load of 12 N and different sliding velocities. The results show that the friction coefficient and wear rate increase with increasing sliding velocity from 0.2 to 0.4 m/s due to the adhesion between the sliding bodies and tearing of the graphene layer. The friction coefficient and wear rate tend to decrease at a sliding velocity of 0.6 m/s as a result of severe plastic deformation and grain refinement of the worn surface. However, at 0.8 m/s the friction coefficient reaches a minimum value and the wear rate increases and changes the wear mechanism to fatigue wear. It can be concluded that various wear mechanisms lead to different tribological performance of NiAl–1.5 wt% graphene composite.

Tribological properties of TiAl matrix self-lubricating composites incorporated with tungsten disulfide and zinc oxide

To better understand the temperature-adjusted action of tungsten disulfide (WS2) and zinc oxide (ZnO) in self-lubricating composites, dry sliding tribological properties of TiAl matrix self-lubricating composites (TMSC) containing WS2, ZnO and WS2–ZnO against Si3N4 counterface are comparatively investigated from 25 to 800 °C. Tribological results suggest that TMSC containing WS2–ZnO exhibit the lowest friction coefficients and wear rates than TMSC containing only WS2 or ZnO over the wide temperature range, confirming the self-adjusted action of WS2–ZnO as the temperature changes. Specifically, WS2 is beneficial to the improvements of tribological properties within 200 °C, WS2 and ZnWO4 for 400 °C, ZnWO4 and ZnO for 600 °C and ZnO for 800 °C.

Wear and Friction of TiAl Matrix Self-Lubricating Composites against Si3N4 in Air at Room and Elevated Temperatures

More durable, low-friction bearing materials over a wide temperature range are needed for turbine components and other high-temperature bearing applications. The current study reported the tribological properties of TiAl matrix self-lubricating composites (TMC) containing MoS2 (a low-temperature lubricant, below 500°C), hBN (a medium-temperature lubricant, below 600°C), and Ti3SiC2 (a high-temperature lubricant, above 600°C) designated as MhT against an Si3N4 counterface at temperatures ranging from 25 to 800°C in air. The load was 10 N and the sliding speed was 0.2 m/s for all tests. Tribological studies indicated that TMC containing MhT showed a lower friction coefficient and wear rate in comparison to TiAl-based alloy at all test temperatures, which was attributed to the excellent synergetic lubricating effect of MoS2, hBN, and Ti3SiC2. TMC containing 5 wt% MhT exhibited the best tribological properties over a wide temperature range.

Formation of Friction Layers in Graphene-Reinforced TiAl Matrix Self-Lubricating Composites

The friction layer structure has been proved to be formed during severe plastic deformation and markedly improves the tribological properties of material. The dry friction and wear performance of graphene-reinforced TiAl matrix self-lubricating composites (GTMSC) at different sliding velocities are systematically researched. GTMSC show the best tribological properties and special friction layer structure containing a wear-induced layer and a grain refinement layer with a nanocrystalline (NC) structure under surface after sliding at a sliding speed of 1.1 m/s. Nanoindentation results show that the grain refinement layer has a higher hardness and elastic modulus than the wear-induced layer. This special microstructure of friction layers beneath the surface after sliding leads to a low coefficient of friction and high wear resistance of GTMSC. Moreover, it is deduced that the appearance of an NC structure results in hardening of the material. The formation mechanisms of friction layers are researched in detail. It can be concluded that the formation of a wear-induced layer results from frictional heat and fracture of the counterpart. The formation of a grain refinement layer is due to severe plastic deformation and dynamic recrystallization. Severe plastic deformation results in the formation of an NC structure and dynamic recrystallization leads to grain refinement.

Friction and Wear Properties of TiAl-Ti3SiC2-MoS2 Composites Prepared by Spark Plasma Sintering

TiAl matrix self-lubricating composites (TMC) with various weight percentages of Ti3SiC2 and MoS2 lubricants were prepared by spark plasma sintering (SPS). The dry sliding tribological behaviors of TMC against an Si3N4 ceramic ball at room temperature were investigated through the determination of friction coefficients and wear rates and the analysis of the morphologies and compositions of wear debris, worn surfaces of TMC, and the Si3N4 ceramic ball. The results indicated that TMC with 10 wt% (Ti3SiC2-MoS2) lubricants had good tribological properties due to the unique stratification subsurface microstructure of the worn surface. The friction coefficient was about 0.57, and the wear rate was 4.22 × 10−4 mm3 (Nm)−1. The main wear mechanisms of TMC with 10 wt% (Ti3SiC2-MoS2) lubricants were abrasive wear, oxidation wear, and delamination of the friction layer. However, the main wear mechanisms of TMC without Ti3SiC2 and MoS2 lubricants were abrasive wear and oxidation wear. The continuous friction layer was not formed on the worn surfaces. The self-lubricating friction layer on the frictional surface, different phase compositions and hardness, as well as density of TMC contributed to the change in the friction coefficient and wear rate.

Synergetic Lubricating Effect of WS2 and Ti3SiC2 on Tribological Properties of Ni3Al Matrix Composites at Elevated Temperatures

The tribological behaviors of the Ni3Al-WS2-Ti3SiC2 composites and synergistic effect of composite solid lubricants are investigated from room temperature to 800°C. The results show that the Ni3Al matrix composites (NASC) exhibit excellent tribological properties throughout the test temperatures compared to Ni3Al-based alloy. The excellent tribological properties of NASC are attributed to the synergistic lubricating effect of WS2 and Ti3SiC2. A lubricating film could be formed below 400°C, and an oxidation protection film is formed above 400°C on the worn surface of NASC during the sliding process, leading to low coefficients of friction (0.18–0.39) and wear rates (1.5–3.7 × 10−5 mm3N−1m−1).

Analytical model and experimental validation of the local damage mechanism of solid lubricant films for metal matrix self-lubricating composites

To explore the local damage mechanism of solid lubricant films for metal matrix self-lubricating composites, a simplified model for analyzing sliding friction contact and a mathematical model for calculating surface stresses of solid lubricant films are built. Based on the analytical model, we have investigated the local damage mechanisms of solid lubricant films under different theoretical and experimental conditions. Theoretical analyses suggest that surface damages can still occur in the local regions of solid lubricant films under a low normal load or a low friction coefficient; the damage degrees are aggravated and the damage mechanisms change with an increase in normal load and friction coefficient; and the sliding friction contact of TiAl matrix composites against GCr15 steel may be a desirable design. Finally, sliding friction experiments have been carried out and experimental results are found to be in qualitative agreement with theoretical analyses, validating the accuracy of the analytical model.

Tribological Behaviors of NiAl-Ti3SiC2 Self-Lubricating Composites at Elevated Temperatures

The tribological behaviors of NiAl-Ti3SiC2 composites (NMC) against Si3N4 at elevated temperatures were investigated by carrying out dry sliding wear tests at the condition of 10 N–0.2 m/s. The results showed that NMC without Ti3SiC2 had a high friction coefficient and wear rate at elevated temperatures, and the addition of Ti3SiC2 could improve the high-temperature tribological properties. Both the friction coefficient and wear rate of NMC obviously decreased at 600 and 800°C with the addition of Ti3SiC2. The excellent tribological behaviors of NMC with 5 wt% Ti3SiC2 at elevated temperatures implied that 5 wt% Ti3SiC2 could be the optimal content.