In this paper, we review recent research developments regarding the tribological performances of a series of inorganic nano-additives in lubricating fluids. First, we examine several basic types of inorganic nanomaterials, including metallic nanoparticles, metal oxides, carbon nanomaterials, and "other" nanomaterials. More specifically, the metallic nanoparticles we examine include silver, copper, nickel, molybdenum, and tungsten nanoparticles; the metal oxides include CuO, ZnO, Fe₃O₄, TiO₂, ZrO₂, Al₂O₃, and several double-metal oxides; the carbon nanomaterials include fullerene, carbon quantum dots, carbon nanotubes, graphene, graphene oxides, graphite, and diamond; and the "other" nanomaterials include metal sulfides, rare-earth compounds, layered double hydroxides, clay minerals, hexagonal boron nitride, black phosphorus, and nanocomposites. Second, we summarize the lubrication mechanisms of these nano-additives and identify the factors affecting their tribological performance. Finally, we briefly discuss the challenges faced by inorganic nanoparticles in lubrication applications and discuss future research directions. This review offers new perspectives to improve our understanding of inorganic nano-additives in tribology, as well as several new approaches to expand their practical applications.

The tribological behaviors of two types of seal coatings, nickel–graphite and aluminum–hexagon-boron nitride (Ni–Cg and Al–hBN, respectively) versus a Ti–6Al–4V blade used in turbofan engines were investigated using a high-speed rubbing test. The wear status and damage mechanism of the friction couples were studied and the abradability of the seal coatings was evaluated. By analysis of the coating properties and damage mechanism of the seal couple, the friction heat effect was identified as the key factor influencing blade wear forms as well as coating abradability. A one-dimensional heat conduction model was established to estimate the effect of increasing temperature on the friction interface. The results indicated that in the Ni–Cg and Ti–6Al–4V seal couple, the temperature rising rate (TRR) of the Ti–6Al–4V blade was faster than that of the Ni–Cg coating, and so the Ti–6Al–4V blade softened earlier than the Ni–Cg coating, causing the blade to suffer severe wear. In the Al–hBN and Ti–6Al–4V seal couple, the TRR of the Ti–6Al–4V blade was slower than that of the Al–hBN coating, and so the Al–hBN coating softened first; thus, blade damage was reduced or even replaced by coating adhesion. The square root ratio of thermal diffusivity between the blade and the coating could be taken as an indicator of the ratio of TRR between the blade and coating to predict blade wear status as well as damage mechanism. The results of the model agreed well with the experiment results of the two seal couples used in this study.