Ultra-high temperature ceramics refer to ceramic matrix composite materials that can be used above 1800°C and have excellent high-temperature oxidation resistance and thermal shock resistance. Ultra-high temperature ceramics can adapt to extreme environments such as ultra-high speed long-term flight, atmospheric reentry, trans-atmospheric flight and rocket propulsion systems, and can be used in various key parts or components such as aircraft nose cones, wing leading edges, and engine hot ends.
Ultra-high temperature ceramics are mainly composed of high melting point borides and carbides. Among them,
HfB2,
ZrB2,
HfC,
ZrC,
TaC and other borides and carbides have melting points of more than 3000℃, no phase change, and excellent thermochemical stability. Performance and excellent physical properties, including high elastic modulus, high hardness, low saturated vapor pressure, high thermal conductivity and electrical conductivity, moderate thermal expansion rate and good thermal shock resistance, and can maintain high performance at high temperatures strength.
At present, the commonly used ultra-high temperature ceramics mainly include ceramic matrix composite materials, carbide ceramics, boride ceramics and nitride ceramics.
Ceramic matrix composite
The research of ceramic matrix composites mainly focuses on Cf/SiC and SiCf/SiC composites. Dong Shaoming of the Shanghai Institute of Ceramics, Chinese Academy of Sciences, and others tried to add boron, aluminum and other additives in the process of preparing Cf/SiC and SiCf/SiC composites by PIP, which achieved the goal of shortening the densification time of PIP and improving the oxidation resistance and mechanical properties. Effect.
Carbide ultra-high temperature ceramics
Currently commonly used carbide ultra-high temperature ceramics mainly include SiC, ZrC, TaC and HfC. The research of carbide ultra-high temperature ceramics mainly focuses on the preparation of layered carbide ultra-high temperature ceramics with better performance, and the effect of adding additives on the performance of ceramics. The ZrC-SiC-C ceramics containing 20% SiC and 10% graphite prepared by Ma et al. using the hot-press sintering method have a bending strength of 425 MPa at room temperature, and can maintain about 63.5% of the original strength after thermal shock at 300 ℃ .
Boride ultra-high temperature ceramics
Compared with carbides and nitrides, boride ultra-high temperature ceramics have more excellent oxidation resistance. In recent years, the research on boride ultra-high temperature ceramics has mainly focused on the densification process, the improvement of mechanical properties and the oxidation resistance. Boride ultra-high temperature ceramics mainly include ZrB2,
TaB2 and HfB2.
Nitride UHT Ceramics
Nitride UHT ceramics have stable chemical properties, mostly covalent bonds, and the structural unit is tetrahedral M4N, which is similar to diamond and is also called a diamond-like compound. The most widely used nitride ultra-high temperature ceramics mainly include Si3N4,
BN and
HfN.
Ultra-high-temperature ceramic matrix composites are promising materials in the field of ultra-high temperature in the future due to their potential excellent high-temperature comprehensive performance. The development of basic material science research and high-end technical science research for them has important scientific significance and application value.
(Chat Online)