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What are the factors that affect the wear resistance of ceramics?

Wear-resistant ceramic materials are widely used in grinding and polishing materials, wear-resistant coatings, pipe or equipment lining, structural parts and other fields, and its wear-resistant performance directly determines the safe service life of mechanical equipment and parts. Common wear-resistant ceramic materials are zirconia, alumina, cubic boron nitride, silicon nitride, boron carbide, silicon carbide and so on.

In order to obtain better wear resistance ceramic materials, many scholars have studied the wear mechanism of ceramic materials and the factors affecting the wear resistance of ceramics. Generally speaking, the wear resistance of ceramics is affected by two factors, one is the structure of the material itself, and the other is external factors such as load, temperature, and atmosphere.

1. the effect of mechanical properties on the wear resistance of ceramics

In the early research on the wear resistance of ceramic materials, it is believed that the hardness of ceramic materials is closely related to the wear resistance. It was later found that the relationship between hardness and wear of ceramics was not so obvious. For example, the hardness of alumina ceramics is higher than that of zirconia ceramics, but the wear resistance is not necessarily higher than that of zirconia ceramics. Although hardness can reflect the binding strength of grain boundaries to a certain extent, wear is ultimately formed by the material separating from the wear surface, so the hardness of ceramic materials is no longer used as a predictor of wear. Studies have shown that with the increase of fracture toughness and hardness of the material, the wear rate of the ceramic is gradually reduced, and the wear resistance is better.

2. the effect of microstructure on the wear resistance of ceramics

In general, the microstructure of the material often has a great impact on the macroscopic properties of the material. Ceramic materials are sintered bodies composed of grains and intergrains, and their microstructure often determines their macroscopic properties. Many studies have shown that the wear resistance of ceramic materials is closely related to the grain size, grain boundary phase composition, grain boundary stress distribution, porosity and other microstructure.

3. Grain

In industry, metal materials can improve their mechanical properties by refining their grains, which is called fine grain strengthening. The main principle is that the smaller the grain size, the larger the grain boundary area, the more jagged the grain boundary distribution, which can effectively increase the crack propagation path and is conducive to stress concentration in dispersed materials. It is found that grain refinement has a certain effect on the wear resistance of ceramic materials.

4. Porosity

Porosity has a very important effect on the properties of ceramics. The existence of pores is equivalent to defects, which will cause stress concentration, accelerate crack growth, reduce the bonding strength between grains, and seriously affect the mechanical properties of ceramics. Under the action of friction, the pores may connect with each other to form crack sources and accelerate material wear.

5. grain boundary phase and intergranular impurities

Ceramics are composed of grain, grain boundary phase and porosity. In the sintering process, some additives and impurities added to ceramics mainly exist in the form of "second phase" or "glass phase" at the grain boundary, and their presence will affect the bonding strength between grains. In the process of ceramic friction and wear, cracks are easy to occur at grain boundaries. The grain boundary bonding strength is low, which will cause the fracture along the grain during the wear process, resulting in the whole grain being pulled out, resulting in serious wear.

Additives to polycrystalline ceramics usually exist at the grain boundaries in the form of a glass phase. During friction, the resulting high temperature reduces the viscosity of the glass, resulting in plastic deformation. If the stress of adjacent grain boundaries is inappropriate, cracks will occur at the grain boundaries, causing serious wear.

If the appropriate amount of additives can form a second phase at the grain boundary, it is usually conducive to the wear resistance of the material. For example, zirconia is added to alumina to make zirconia toughened alumina ceramics, also known as ZTA ceramics. Because the increase of critical stress induced by T-ZrO2 stress is conducive to the improvement of fracture toughness and strength of ceramic materials, zirconia and alumina can inhibit the grain growth and achieve the effect of microcrystallization in the microstructure, so as to further improve the wear resistance.

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