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Rocket Engines
Published in Ahmed F. El-Sayed, Aircraft Propulsion and Gas Turbine Engines, 2017
Core design is a very complicated procedure that includes thermal, mechanical, and nuclear design procedures. Furthermore, control mechanisms must be provided to start up, regulate, and shut down the system on demand. Since the core material must perform at a very high temperature, selected materials must have a very high melting point like graphite (7050° R), zirconium carbide (6880° R), hafnium carbide (7500° R), and tantalum carbide (7460° R).
Paths to the Energy Miracles
Published in H. B. Glushakow, Energy Miracles, 2022
Active volcanoes also provide direct access to an almost unlimited source of extreme heat. It needs some careful design work and some clever application of material science, but the potential is there to create electrical current from every one of Earth’s active volcanoes. Materials such as tantalum carbide (TaC) and hafnium carbide (HfC) have already been developed that can withstand temperatures of 4000°C.
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.
Wear of friction stir tools considering qualitative and quantitative aspects: a review
Published in International Journal of Ambient Energy, 2022
Several tools and techniques are widely implemented to quantify the tool wear and to characterise the microstructure, including thermo mechanical modelling (Gan et al. 2007), CFD model (Hasan et al. 2017; Colegrove and Shercliff 2006), 3D ABAQUS FE model (Colegrove and Shercliff 2006), 3D scanning model (Siddiquee and Pandey (2014), three-dimensional HTMF numerical model Sahlot and Arora (2018). Besides these, various approaches are adopted by to characterise the microstructures, such as Archard’s wear hypothesis (Hasan et al. 2017), acoustic emission (AE) sensing (Zeng, Wu, and Zhang (2006), abrasion and diffusion mechanism (Konig and Neises 1993), degradation mechanism (Thompson 2010), SEM (Sahlot et al. 2018). Hasan et al. (2017) calculated tool wear rate of tungsten – rhenium – hafnium carbide (W-Re-HfC) tool material during FSW of AISI 304 austenitic stainless steel. As shown in Figure 9, a CFD model analysed the pressure distribution generated by the flow of material during the process. This pressure distribution is responsible for the wear on the tool which is increased by tool rotational speed. As there is a rapid change of flow at the shoulder edge swear rate becomes more at shoulder.
Radiation-induced phase separation in nanostructured Hf-In-C ternary thin films under irradiation with 200 keV Ar+ ion beam
Published in Radiation Effects and Defects in Solids, 2022
Jiri Vacik, Antonino Cannavò, Snejana Bakardjieva, Jaroslav Kupcik, Vasily Lavrentiev, Giovanni Ceccio, Pavel Horak, Jiri Nemecek, Alessio Verna, Matteo Parmeggiani, Lucia Calcagno, Robert Klie, Jan Duchoň
It should be noted that other compounds may also be expected in the samples. The most probable are hafnium carbide-oxides with the cubic structure like HfC0.84O0.16 (26) or monoclinic HfCxO2−x (27), cubic Hf/C with non-stoichiometric composition (different by the cell parameter). Also, hafnium sub-oxides (hexagonal HfO0.25 and others), In2O3 rhombohedral, pure Hf or crystalline C, can be considered. However, these structures can be omitted. The used HfC structure can be considered as a representative of all cubic carbides and oxide-carbides because they have the same Fm-3 m structure and their cell parameters (26) do not differ more than 5% declared as accuracy for TEM methods. The same can be said about monoclinic oxide-carbides HfCxO2−x. Their cell parameters (27) do not differ much from monoclinic HfO2, which can be used as their representative. Sub-oxide HfO0,25 was tried but its occurrence was found as negligible (<1%). Also, rhombohedral In2O3 can be found in the Ar_15 sample, but in negligible amounts, and in Pristine it is not probable (it is formed at very high temperatures). The occurrence of pure Hf in a significant amount in any sample is unlikely.