A group of scientists of NUST “MISiS” developed a ceramic material with the highest melting point among all currently known compounds. Due to the unique combination of physical, mechanical and thermal properties, the material is promising for use in the most heat-loaded units of aircraft – nose fairings, air-jet engines and sharp leading edges of wings operating at temperatures above 2000 ° С.
“Currently, significant results have been achieved in the development of videoconferencing. For example, reducing the radius of rounding of the sharp leading edges of the wings to a few centimeters leads to a significant increase in lift and maneuverability, and also reduces aerodynamic drag. However, when leaving the atmosphere and re-entering, temperatures of the order of 2000 ° С can be observed on the surface of the VKS wings, and 4000 ° С on the very edge. Therefore, when it comes to such aircraft, the question arises related to the creation and development of new materials that can operate at such high temperatures, ”comments Director of the Research Center for Structural Ceramic Nanomaterials NITU MISiS Dmitry Moskovsky.
In the course of recent developments, the task of the Center’s scientists was to create a material with a record high melting point and high mechanical properties. The hafnium-carbon-nitrogen triple system, hafnium carbonitride (Hf-CN), was chosen as a candidate, since previously, scientists from Brown University (USA) using molecular dynamics predicted that hafnium carbonitride would have high thermal conductivity and oxidation resistance, and also the highest melting point among all known compounds (approximately 4200 ° C).
Using the method of self-propagating high-temperature synthesis, scientists of NUST “MISiS” were able to obtain material HfC0.5N0.35, (hafnium carbonitride) close to the theoretical composition, with a high hardness of 21.3 GPa, which is not inferior to other promising materials, such as ZrB2 / SiC (diboride zirconium-silicon carbide) (20.9 GPa) and HfB2 / SiC / TaSi2 (hafnium diboride-silicon carbide-tantalum dyslenide) (18.1 GPa).
“It is difficult to measure the melting point of a material when it exceeds 4000 ° C,” comments graduate student Veronika Buynevichwhose research topic is “Obtaining ultrahigh-temperature ceramics based on hafnium carbonitride for operation in extreme conditions”. – Therefore, we made a decision to compare the melting points of the synthesized compound and the initial “champion” – hafnium carbide. To do this, we placed pressed samples of HfC and HfCN on a dumbbell-shaped graphite plate, covered with a similar plate on top to avoid heat loss. “
The resulting “sandwich” scientists connected to a powerful battery using molybdenum electrodes. All tests were carried out in a deep vacuum. Since the cross section for graphite plates is different, the maximum temperature was reached in its narrowest part. The results of simultaneous heating of a new material, hafnium carbonitride and carbide showed that carbonitride has a higher melting point than hafnium carbide.
However, at the moment, it was not possible to determine the specific melting temperature of the new material above 4000 ° C – it is very difficult to simulate such temperature loads in laboratory conditions. In the future, the team plans to conduct experiments to measure the melting temperature by high-temperature pyrometry when melting with a laser or electrical resistance. It is also planned to study the “operability” of the obtained hafnium carbonitride in hypersonic conditions, which will be relevant for further use in the aerospace industry.