Using the method of self-propagating high-temperature synthesis, NUSTMISIS scientists created HfC0.5N0.35, (hafnium carbonitride) which is close to a desired theoretical composition. It has a high hardness of 21.3 GPa and can withstand temperatures over 4000 degrees celsius.
The hardness is higher than in other promising materials, such as ZrB2/SiC (20.9 GPa) and HfB2/SiC/TaSi2 (18.1 GPa).
Brown University (U.S.) had previously predicted that hafnium carbonitride would have a high thermal conductivity and resistance to oxidation, as well as the highest melting point among all known compounds (approximately 4200 degrees C).
The specific melting point of the new material is above 4000 degrees C, and could not be determined precisely in the laboratory. In the future, the team plans to conduct experiments on measuring the melting temperature by high-temperature pyrometry using a laser or electric resistance. They also plan to study the performance of the resulting hafnium carbonitride in hypersonic conditions, which will be relevant for further application in the aerospace industry.
Nonstoichiometric hafnium carbonitrides (HfCxNy) was fabricated via short-term (5 min) high-energy ball milling of Hf and C powders, followed by combustion of mechanically induced Hf/C composite particles in a nitrogen atmosphere (0.8 MPa). The obtained HfC0.5N0.35 powder exhibited a rock-salt crystal structure with a lattice parameter of 0.4606 nm. The melting point of this synthesized ceramic material was experimentally shown to be higher than that of binary hafnium carbide (HfC). The nonstoichiometric hafnium carbonitride was then consolidated under a constant pressure of 50 MPa at a temperature of 2000 °C and a dwelling time of 10 min, through spark plasma sintering. The obtained bulk ceramic material had a theoretical material density of 98%, Vickers hardness of 21.3 GPa, and fracture toughness of 4.7 MPa m1/2
SOURCES- Phys Org, Ceramics International
Written By Brian Wang, Nextbigfuture.com