The tribological behavior of zinc phosphate impregnated graphite (ZPIG) against nickel-based superalloy (GH4169) in oil environment was investigated, and the lubrication and wear mechanism were also determined in this study. Tribological tests were run under different tribological conditions using a ring-on-disk device. The results showed that, under any load conditions, zinc phosphate impregnated graphite had the lowest coefficient of friction (COF) and wear-rate at 200 rpm. Under the identical rotating speed condition, the minimum coefficient of friction and wear-rate were obtained when the load was 500 N and 1000 N. The lubrication mechanism, which could be reflected by the transfer layer of friction counterpart, was related to the coefficient of friction, wear-rate, and oil temperature to affect contact characteristics of two solid surfaces and formation ability of liquid film. The wear mechanism of zinc phosphate impregnated graphite under oil lubrication conditions was dominated by abrasive wear and material removal was achieved through the fracture mechanism.

The stability of the graphite seal device is a key factor for the normal operation of aero engines. However, conventional graphite exhibits poor comprehensive performance due to its porous structure, which limits its application at high temperatures. Therefore, in this paper, phosphate was used to impregnated graphite pores, and the interaction between the friction, wear, and oxidation of phosphate-impregnated graphite against superalloy at high temperatures was studied through pin-on-disk friction tests. The results revealed that the coefficient of friction (COF) of matrix graphite fluctuated greatly, from 0.07 to 0.17, in the range of 100 °C to 500 °C, while the COF of impregnated graphite was stable, at around 0.13, from 100 °C to 500 °C. The wear rates of the two types of graphite were close from 20 °C to 300 °C, while the wear rate of the impregnated graphite was significantly lower than that of the matrix graphite at higher temperatures, from 400 °C and 500 °C. The reason was that the impregnated phosphate reacted with graphite at a high temperature, forming the inert site which helped to inhibit the oxidation and maintain the mechanical properties of the impregnated graphite at high temperatures. In addition, the impregnated graphite could maintain better integrity of the contact surface and reduce the inclusion of large hard metal oxides, thus effectively reducing the abrasive wear of the disk. Therefore, the wear depth of the superalloy disk samples with impregnated graphite was significantly lower than that of the matrix graphite. The results promote the application of phosphate-impregnated graphite under the high temperature conditions of aero engines.

Several criteria for fretting wear behavior evaluation have been established since the proposal and establishment of the fretting loop concept. In this article, system deformation and system deformation ratio were defined. In addition, the fretting running conditions were distinguished from the evolution of system deformation with fretting cycles during fretting wear tests under different applied displacements and loads. In the gross slip regime, the system deformation was independent of the applied displacement and increased as the load increased, whereas in the partial slip regime, the system deformation was independent of the load and increased with the applied displacement. Furthermore, a linear relationship between the system deformation and the applied load in gross slip regime was found for the first time. Based on this linear relationship, the system deformation ratio can forecast the running regime with a given load and displacement. For the titanium alloy fretting pairs studied in this article, the fretting wear was found to run in the gross slip regime if the system deformation ratio was smaller than 0.9. Based on these observations, the system deformation ratio exhibited applicability in assisting the mechanical design of equipment suffering from fretting wear.

A novel NiAlTa/cBN composite produced by spark plasma sintering exhibited exceptional wear resistance, which is attributed to the tribo-layers with special nano-heterostructures. At room temperature, an extremely low wear rate (10⁻⁷ mm³·N⁻¹·m⁻¹) and a low coefficient of friction (0.252) of the composite were attributed to the nanoscale amorphous tribo-layer. Amorphization was synergistically controlled by the solid-state amorphization and oxidation processes. The amorphous tribo-layer accommodated the sliding-induced elastic–plastic deformation and virtually eliminated wear. At high temperatures, the plastic incompatibility and strain localization of the subsurface nanocrystalline layer increased the wear rate. The formation of an amorphous tribo-oxide layer and oxidative cleaving effect reduced the fracture toughness of cBN particles and increased the tendency of crack nucleation and growth. Multiple deformation pathways synergistically increased the microplastic deformability of cBN particles and reduced the wear rate. Ta₃N₅ nanoparticles generated by tribo-chemical reactions played a load-supporting and stress-transferring role in sliding wear. A strategy to achieve exceptional wear resistance by regulating the evolution of specific nano-heterostructures on the composite surfaces was proposed. Graphical abstract