Brief Analysis of Factors Affecting Wear Resistance of Ceramic Materials

Wear-resistant ceramic materials are widely used in grinding and polishing materials, wear-resistant coatings, pipelines or equipment linings, equipment structural parts, etc. The quality of their wear resistance directly determines the safe service life of mechanical equipment and parts. Common wear-resistant ceramic materials include diamond, zirconia, cubic boron nitride, silicon nitride, boron carbide, silicon carbide, various corundum and so on.

In order to obtain wear-resistant ceramic materials with better wear resistance, many scholars have studied the wear mechanism of ceramic materials and the factors affecting the wear resistance of ceramic materials, and put forward many opinions and conclusions. In general, there are two factors that affect the wear resistance of ceramics: 1. The structure of the material itself; 2. External factors such as load, temperature and atmosphere. In this paper, starting from the material's own structure, the factors affecting the wear resistance of wear-resistant materials are briefly analyzed.

1. Influence of mechanical properties on wear resistance of ceramics

When the wear resistance of ceramic materials was studied in the early days, it was believed that the hardness of ceramic materials had a great relationship with the wear performance. Later, it was found that the relationship between the hardness and wear of ceramic materials was not so obvious. For example, the hardness of alumina ceramics is higher Compared with TZP zirconia ceramics, the wear resistance is not necessarily higher than that of TZP ceramics.

Although hardness can reflect the bonding strength of grain boundaries to a certain extent, wear is ultimately formed due to the separation of materials from the wear surface, so the hardness of ceramic materials is no longer a predictive indicator for measuring wear.

It has also been reported that the brittleness of ceramic materials directly affects the wear rate. Studies have shown that as the fracture toughness and hardness of the material increase, the wear rate of ceramics gradually decreases, and the wear resistance is better.

Second, the effect of ceramic microstructure on wear resistance

Usually, the microstructure of the material often has a great influence on the macroscopic properties of the material. Ceramic materials are sintered bodies composed of grains and intergranulars, and their microstructure often determines their macroscopic properties. Many studies have shown that the wear resistance of ceramic materials has a great relationship with the size of the grains, the composition of the grain boundary phase, the stress distribution on the grain boundary, the pores and other microstructures.

1 Effect of grain size on wear resistance of ceramics

Industrially, metal materials can improve their mechanical properties by refining grains, which is called grain refinement strengthening. The principle is that the smaller the grain size of the grain, the larger the area of the grain boundary, and the more tortuous the distribution of the grain boundary, which can effectively increase the path of crack propagation and help to disperse the stress concentration phenomenon inside the material. It has been found through research that grain refinement also has a certain influence on the wear resistance of ceramic materials.

Scholars have studied the wear resistance of alumina and zirconia and found that the smaller grains are mainly plastic deformation and some transgranular fractures, and the wear is less; the larger grains are intergranular fractures inside the material, Even larger wear occurs in the way that large grains are pulled out from the inside of the material. The pull-out of large-sized grains will cause large defects on the ceramic surface, which will easily cause stress concentration of the material, cause crack propagation, and cause low-stress brittle fracture of the material.

2 Effect of porosity on wear resistance of ceramics

The pores have a very important influence on the performance of ceramics. The pores are equivalent to the existence of a defect, which will cause stress concentration, accelerate the expansion of cracks, reduce the bonding strength between grains, and seriously affect the mechanical properties of ceramic products. Under the action of friction, the pores may connect with each other to form crack sources and accelerate the wear of the material.

In addition, some studies have found that the wear rate of ceramics is different under different loads, and the pores will not cause crack propagation at low loads; while under high loads, the pores become unstable and will form at the pores. Cracks and extended cracks lead to extremely high wear rates of products and weakened resistance to sudden changes in wear.

3 The influence of grain boundary phase and intergranular impurities

Ceramics are composed of grains, grain boundary phases and pores. During the sintering process, some additives and some impurity components added to the ceramics mainly exist in the form of "second phase" or "glass phase" at the grain boundary. On the other hand, their existence will have a certain influence on the bonding strength between the grains. In the process of ceramic friction and wear, cracks are easily generated at the grain boundaries. The lower bonding strength of grain boundaries will cause intergranular fracture during the wear process, causing the pull-out of the entire grain, resulting in severe wear.

The additives of polycrystalline ceramics generally exist in the form of glass phase on the ceramic grain boundaries. In the process of friction, the high temperature generated will reduce the viscosity of the glass, thereby causing plastic deformation. If the stress of the adjacent grain boundaries cannot be adapted, it will be Initiates cracks at grain boundaries, causing severe wear.

If an appropriate amount of additives can form a second phase at the grain boundary, it is often beneficial to the wear resistance of the material. For example, in the case of alumina ceramics, due to the anisotropic growth of the grains, there will be residues at the grain boundaries. When the rare earth additive Sm2O3 is added, it can effectively promote the formation of the second phase calcium hexaaluminate on the grain boundary, reduce the content of glass phase at the grain boundary, and effectively alleviate the grain boundary caused by different thermal expansion coefficients. The stress concentration at the place increases the bonding strength of grain boundaries, so that the wear resistance of ceramics is improved.