Brittleness is another essential feature to consider when evaluating the performance of ceramic materials, and it is a frequent fatal flaw of ceramic materials. The visible expression of ceramic brittleness is: under external pressure, the fracture is unexpected and bursts out. The indirect performance is as follows: weak resistance to mechanical stress and fast temperature fluctuations.
Ceramic brittleness is primarily influenced by the type of chemical bonding and crystal structure. Ceramics lack an independent slip system. Once a material has been stressed, it is difficult to release the tension via plastic deformation produced by slip. Brittleness is caused by the presence of micro-cracks, which are prone to high stress concentration, and subsequently micro-cracks spread and shatter. The following is the characteristics introduction of the brittleness of ceramic materials.
1. Covalent Bond Characteristics
There are numerous gaps between the atoms that make up the chemical bonds in ceramic materials, making it harder to induce dislocation movement. The covalent bond possesses directionality, which complicates the crystal structure, and it has a greater capacity to resist deformation and impede unique mobility.
2. Microstructure Characteristics
Ceramic materials are polycrystalline and have a multi-phase structure. Its grain boundaries will prevent displacement, and aggregate displacement will result in the development of fractures. In addition to the presence of point, line, and surface flaws in the real crystal structure, there are also microscopic and sub-microscopic fractures, and structural inhomogeneity is unavoidable. Furthermore, microstructure features such as grain boundaries, pores, crystal phases, two-phase inclusions, and fractures may all contribute to the brittleness of ceramic materials.
3. No Plastic Deformation Characteristics
Most ceramic materials exhibit little or only minor plastic deformation under the application of external force at normal temperature, causing the ceramic materials to shatter abruptly, causing them to seem brittle.
Brittle fracture is a stress redistribution process that occurs when a material is stressed below its own bonding strength, and when the rate of applied stress exceeds the rate of stress redistribution, there is no other process of absorbing energy, and the stress cannot be relaxed, so concentrated use is required. The growth of fractures occurs at a very fast rate, resulting in abrupt destruction. Brittle fracture marks the conclusion of crack growth.
