Yecheng Xiao

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.

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.

Effect of Temperature on Tribological Properties and Wear Mechanisms of NiAl Matrix Self-Lubricating Composites Containing Graphene Nanoplatelets

Studies have been carried out to explore the friction and wear behaviors of NiAl matrix self-lubricating composites containing graphene nanoplatelets (NG) against an Si3N4 ball from 100 to 600°C with a normal load of 10 N and a constant speed of 0.2 m/s. The results show that NG exhibits excellent tribological performance from 100 to 400°C compared to NiAl-based alloys. A possible explanation for this is that graphene nanoplatelets (GNPs) contribute to the formation of a friction layer, which could be beneficial to the low friction coefficient and lower wear rate of NG. As the temperature increases up to 500°C, the beneficial effect of GNPs on the tribological performance of NG becomes invalid due to the oxidation of GNPs, resulting in severe adhesive wear and degradation of the friction layer on the worn surface of NG. GNPs could hold great potential applications as an effective solid lubricant to promote the formation of a friction layer and prevent severe sliding wear below 400°C.

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).

Tribological Performance of Ni3Al Self-Lubricating Composites with Different Content of TiC at Elevated Temperature

Ni3Al-MoS2-TiC composites (NMTC) were fabricated using spark plasma sintering. The effect of TiC content on tribological properties and antiwear mechanisms of NMTC at high temperatures was investigated. The results showed that NMTC containing 10 wt% MoS2 and 6 wt% TiC exhibited the excellent tribological properties from 25 to 600°C. At 400°C, NMTC had the lowest friction coefficient of 0.28 and the considerable lower wear rate of 3.02 × 10−5 mm3 N−1 m−1. The excellent tribological properties of NMTC were attributed to the synergetic action of the lubricant-phase MoS2 and reinforcing-phase TiC.

Research on the Thickness of the Friction Layer of Ni 3 Al Matrix Composites with Graphene Nanoplatelets

Dry sliding tribological tests of Ni3Al matrix composites (NMCs) with/without graphene nanoplatelets (GNPs) under different working conditions are undertaken in this article. The results show that GNPs in NMCs make a major contribution to the formation of the friction layer, which is responsible for the reduction of the friction coefficient and improvement of wear resistance. In addition, with the increase in the sliding velocity and normal load, the friction coefficient decreases to a stable value and the wear rate increases to a stable value. This article also examines the possibility of describing the formation of the friction layer during the sliding process. The formation of the friction layer can be divided into two processes: the formation of the fine grain layer and the material loss of the surface layer. The strain rate intensity factor is used to describe the formation of the fine grain layer, and the functional relation of the material loss of the surface layer is obtained by the experimental data. As a result, a specific formula for calculating the thickness of the friction layer of NMCs with GNPs is found.

Study on Tribological Performance of NiAl Matrix Self-Lubricating Composites Containing Graphene at Different Loads

ABSTRACT This study aimed to explore the possibility of improving the tribological performance of NiAl matrix composites by graphene addition. Friction and wear experiments of as-prepared specimens were conducted under different conditions using a pin-on-disk wear testing machine. NiAl matrix composites containing graphene showed satisfactory performance in friction coefficient and wear resistance compared to NiAl matrix composites without graphene. For the active effect of graphene, the friction coefficient and wear rate of NiAl matrix composites were maintained at relatively lower values. The beneficial antifriction and antiwear effects of graphene gradually failed when the applied load was above 8 N. Graphene in NiAl matrix composites played an active role in the formation of a friction layer, which was beneficial to the lower friction coefficient and wear rate. In light of this research, graphene plays an active role in reducing the friction coefficient and wear rate. Hence, graphene has great potential in applications as an effective solid lubricant to promote tribological behavior.