Recent Progress in Self-Lubricating Ceramic Composites

Abstract

Structural ceramic composites have received increasing attention over the past few decades for their potential applications in various fields. Lubrication is usually required for moving ceramic parts because of their high coefficient of friction under dry sliding conditions. Self-lubricating ceramic composites have been applied in severe operating conditions where conventional lubrication method, such as liquid lubrication, is unavailable. The solid lubricants added in self-lubricating ceramic composites can reduce the coefficient of friction. However, they decrease mechanical properties and then weaken antiwear property of the ceramic composites, which consequently restricts self-lubricating ceramic composites’ application scope. Therefore, there is a contradiction between the antifriction and antiwear properties of self-lubricating ceramic composites and many efforts from researchers have been devoted to resolve it. In this chapter, two new types of self-lubricating ceramic composites were elaborated. Graded self-lubricating ceramic composites were developed by adopting the design concept of functionally graded materials (FGMs). Their characteristics are that the solid lubricant content decreases with a gradient from the surface to the center and thermal residual compressive stresses exist in the surface after the sintering process. The gradient distribution of solid lubricant and the thermal residual compressive stresses are used to improve the mechanical properties of the ceramic composites. Another new type of self-lubricating ceramic composites is those with the addition of coated solid lubricants. The solid lubricant powders are firstly coated by metal or metallic oxide, etc., to form core-shell structured composite powders and then mixed with the ceramic matrix powders to prepare self-lubricating ceramic composites by sintering. The shell substance is used to protect the solid lubricant core from reacting with the ceramic matrix during the sintering process and promote the relative density of the ceramic composites. The two new types of self-lubricating ceramic composites showed superior mechanical properties and tribological properties to the traditional self-lubricating ceramic composites.