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Contemporary Methods of Protection and Restoration of Components
Published in E. S. Gevorkyan, M. Rucki, V. P. Nerubatskyi, W. Żurowski, Z. Siemiątkowski, D. Morozow, A. G. Kharatyan, Remanufacturing and Advanced Machining Processes for New Materials and Components, 2022
E. S. Gevorkyan, M. Rucki, V. P. Nerubatskyi, W. Żurowski, Z. Siemiątkowski, D. Morozow, A. G. Kharatyan
A distinctive family of ceramic materials has come to be known as ultra-high-temperature ceramics (UHTCs). It includes ceramic borides, carbides and nitrides of early transition metals such as Zr, Hf, Nb, and Ta, especially hafnium diboride and zirconium diboride-based compositions, characterized by high melting points, chemical inertness and relatively good oxidation resistance in extreme environments (Gasch et al., 2005). Fahrenholtz and Hilmas (2017) point out that UHTCs are often defined as compounds that have melting points above 3000°C or, in the most pragmatic way, calling UHTCs ceramic materials that can be used for extended times at temperatures above 1650°C. However, none of these definitions captures the wide range of extreme conditions in which UHTCs may be used. The strong covalent bonds between the transition metals and B, C, or N produce UHTCs not only with melting temperature, but also with high hardness and stiffness, as well as higher electrical and thermal conductivities than that of oxide ceramics. The authors emphasize that the above-mentioned intriguing combination of metal-like and ceramic-like properties allows UHTCs to survive extreme temperatures, heat fluxes, radiation levels, mechanical loads, chemical reactivities, and other conditions that are beyond the capabilities of existing structural materials (Fahrenholtz and Hilmas, 2017).
Introduction of Supersonic Flight
Published in Rose G. Davies, Aerodynamics Principles for Air Transport Pilots, 2020
The kinetic heating can be very intense at certain locations of a supersonic aircraft, for examples, nose of aircraft, leading edge of aerofoil. It can damage the materials and weaken the structure of the aircraft. Many methods to protect the supersonic aircraft from kinetic heating have been developed, and the following are some examples of the methods: Materials: A material can become elastic and the strength of the material will be weakened before its temperature reaches its melting point. The higher its melting point is, the better it tolerates heat. Aluminum is a light metal, but its melting point is about 600°C. Titanium is light, and its melting point is over 1600°C, but it is very expensive. New materials for aircraft have been developed in recent years: alloys with titanium, which would be strong, flexible and can tolerate relatively high temperature. Composite with ceramic matrix is strong and can be used under high temperature environment, but it might not be flexible. Ultra-high-temperature ceramics (UHTCs) developed at NASA contain various metals can be used to protect the surface of high supersonic aircrafts.Insulation: To cover the surface of the body parts, which experience the intensive kinetic heating, with the material, which can withstand high temperature with relatively low thermal conductivity, so heat will not penetrate to the body easily, and protect the flight instrument installed close to the “hot” wall of the body.Surface radiation: To design the structure or shape of surfaces of the body, where are close to the heat sources, to radiate heat easily. The surface with a high emissivity can dissipates the heat quickly; or there is a large area of this surface structure, and the heat can be radiated out, and reduce the thermal load on the surfaces to prevent the local temperature from rapid increasing.Surface cooling: To remove heat from the heated surface or structure of the body can prevent the rising of temperature. Behind the heated surface a jacket or a passage network can be installed, and coolant, which has got a relatively high heat capacity, or high latent heat, is driven through the passage/jacket. The coolant can absorb and transfer the heat from the surface to a heat sink to maintain the temperature in a safe level. For example, water can be used as a coolant, if the surface temperature is not too high.
Preparation and properties of HfB2-HfC and HfB2-HfC-MoB composites by reactive spark plasma sintering
Published in Journal of Asian Ceramic Societies, 2023
Yangshuo Bai, Weixia Shen, Chao Fang, Liangchao Chen, Qianqian Wang, Biao Wan, Xiaopeng Jia, Yuewen Zhang, Zhuangfei Zhang
Hafnium boride (HfB2) and hafnium carbide (HfC) ceramics are regarded as outstanding representatives of the ultra-high-temperature ceramics (UHTCs) family [1] [2, 3]. They are composed of excellent thermally protective materials with high melting points (>3000°C) and high hardness (>20 GPa), chemical stability, and oxidation resistance. This makes them attractive for a variety of structural applications, specifically those with extreme conditions, such as aerospace combustion chambers, rocket nozzles, hypersonic aerospace vehicles and reusable atmospheric reentry vehicles [4, 5]. However, due to their strong covalent bonds and low self-diffusion coefficients, the densification of HfC and HfB2 ceramics is a difficult process [6, 7]. Besides, the very low fracture toughness of HfC and HfB2 is a major application that restricts their wide implementation as structural materials [8]. Addressing these issues is, therefore, a core problem in the further development and application of Hf-based composites.