State of the Art on Self-lubrication of Boron Carbide Ceramics
Self-lubrication of boron carbide(B4C)ceramics significantly influences their tribological properties.However,systematic studies on the mechanism and techniques of self-lubrication of boron carbide ceramics have not been conducted extensively.Boron carbide has high hardness(Vickers hardness is 36 GPa);thus,boron carbide ceramics are potential candidate materials for use as wear-resistant components.However,the friction coefficient of boron carbide ceramics is high,which increases the energy consumption of the frictional system;thus,the widespread application of boron carbide ceramics is limited.Self-lubrication can prevent contamination caused by external lubricants,revealing that the self-lubrication mechanism of boron carbide ceramics can provide a feasible reference for solving the high friction coefficient of boron carbide ceramics.Currently,three methods are mainly used for the self-lubrication of boron carbide ceramics:preoxidation,the addition of solid lubricants,and the construction of a relief structure on the surface.Preoxidation refers to the high-temperature oxidation treatment of boron carbide ceramics in advance in an air environment,which forms an oxide layer comprising B2O3,H3BO3,or both on their surfaces.After the oxidation treatment,H3BO3 with a layered crystal structure or B2O3 generated on the surface of boron carbide ceramics causes a lubrication effect.The residual graphite formed during oxidation may also perform a lubrication function.Although boron carbide ceramics can achieve self-lubrication after a preoxidation treatment,the effect of the preoxidation treatment on the wear rate of boron carbide ceramics is unclear.The reason for applying a solid lubricant is to add a material with a layered crystal structure to the boron carbide ceramic matrix.During the sliding process,the solid lubricant peels off from the boron carbide ceramic matrix and smears on the worn surface of the boron carbide ceramics,forming an external lubricating layer.The wear rate of boron carbide ceramics with solid lubricants is related to the nature of the counterbody.The construction of a surface relief structure involves introducing a second phase with relatively low hardness into the boron carbide ceramic matrix and using the difference in hardness between the boron carbide grains and silicon carbide grains to generate concave and convex surface morphologies in situ during the sliding process.On the one hand,the relief structure formed on the surfaces of boron carbide ceramics can trap wear debris generated during the sliding process,reducing the friction coefficient and abrasive wear.On the other hand,the relief structure can reduce the actual contact area between the boron carbide ceramics and the counterbody,which not only decreases the number of contact points between the boron carbide ceramics and the counterbody,thereby reducing the force required to break these connections,but also reduces the adhesive wear of the boron carbide ceramics.Therefore,the friction coefficient and wear rate of boron carbide ceramics can be reduced by constructing relief structures on their surfaces.Although these self-lubrication methods have technical limitations,they can still achieve self-lubrication of boron carbide ceramics under certain operating conditions,resulting in a decreased friction coefficient of the tribopairs and decreased energy consumption of the friction system.This review summarizes the state of the art on the self-lubrication of boron carbide ceramics in recent years based on the author's research results and proposes future research directions on the self-lubrication of boron carbide ceramics.This review provides useful guidance for the design,research,and application of self-lubrication of boron carbide ceramics.
NETL
NSTL
万方数据
