Ceramic materials are widely used for their corrosion resistance, wear resistance, and high temperature performance. They are a potential high-performance material that can replace metal materials and be used in harsh environments. However, due to the inherent brittleness of ceramic materials, its practical application range is limited. With the continuous progress of science and technology, new ceramic materials have a new development direction.
Ceramic whiskers refer to single crystal fibers with very small diameters. Generally, its length is hundreds of times its diameter, and it is usually grown by the gas phase method. Whiskers have few defects, so their mechanical strength is very high, and their tensile strength can be close to the theoretical strength of pure crystals. The strength of the whiskers is closely related to their thickness. The thicker the whiskers, the lower the strength, so the smaller the diameter of the whiskers, the better. Because whiskers have the characteristics of high strength, low density and heat resistance, they are often used as reinforcing materials. Commonly used whiskers include Al2O3 whiskers, SiC and Si3N4 whiskers, graphite whiskers, etc. Whisker reinforcement is an effective means to improve the high-temperature mechanical properties and thermal shock stability of ceramic materials.
Nanoceramic composite materials were developed in the mid-1980s. Nanoceramic composites can generally be divided into three categories: intragranular, intergranular nanocomposites, and nano/nanocomposites. The nanoscale particles of the first two types of nanocomposites are mainly dispersed within or between matrix grains, and their main goal is to improve high-temperature mechanical properties. Nano/nanocomposites are composed of nanoscale dispersions and matrix grains, aiming to add certain new functions to ceramics, such as processability and superplasticity. The grain size, grain boundary width, second phase distribution, pore and defect size of nanoceramic composite materials are limited to the level of 100nm. The reduction of grain size will double the mechanical properties of the material.
The composition of performance-gradient composite materials gradually changes from one side to the other. The change in composition causes a gradual change in the material performance (or function). This material is a so-called performance-gradient material (called a tilted functional material in Japan). It It is a new material developed by Japan in the mid-1980s. Performance gradient material is a thermal stress relaxation material. It is developed for practical applications that require one side of the material to be heat-resistant and oxidation-resistant, while the other side (cold side) must be tough and be able to relieve and withstand thermal stress. It is a new concept material different from traditional homogeneous composite materials.