1075
Views
315
Downloads
0
Crossref
0
WoS
0
Scopus
0
CSCD
The interest in refractory materials is increasing rapidly in recent decades due to the development of hypersonic vehicles. However, the substance that has the highest melting point (Tm) keeps a secret, since precise measurements in extreme conditions are overwhelmingly difficult. In the present work, an accurate deep potential (DP) model of a Hf–Ta–C–N system was first trained, and then applied to search for the highest melting point material by molecular dynamics (MD) simulation and Bayesian global optimization (BGO). The predicted melting points agree well with the experiments and confirm that carbon site vacancies can enhance the melting point of rock-salt-structure carbides. The solid solution with N is verified as another new and more effective melting point enhancing approach for HfC, while a conventional routing of the solid solution with Ta (e.g., HfTa4C5) is not suggested to result in a maximum melting point. The highest melting point (~4236 K) is achieved with the composition of HfC0.638N0.271, which is ~80 K higher than the highest value in a Hf–C binary system. Dominating mechanism of the N addition is believed to be unstable C–N and N–N bonds in liquid phase, which reduces liquid phase entropy and renders the liquid phase less stable. The improved melting point and less gas generation during oxidation by the addition of N provide a new routing to modify thermal protection materials for the hypersonic vehicles.
The interest in refractory materials is increasing rapidly in recent decades due to the development of hypersonic vehicles. However, the substance that has the highest melting point (Tm) keeps a secret, since precise measurements in extreme conditions are overwhelmingly difficult. In the present work, an accurate deep potential (DP) model of a Hf–Ta–C–N system was first trained, and then applied to search for the highest melting point material by molecular dynamics (MD) simulation and Bayesian global optimization (BGO). The predicted melting points agree well with the experiments and confirm that carbon site vacancies can enhance the melting point of rock-salt-structure carbides. The solid solution with N is verified as another new and more effective melting point enhancing approach for HfC, while a conventional routing of the solid solution with Ta (e.g., HfTa4C5) is not suggested to result in a maximum melting point. The highest melting point (~4236 K) is achieved with the composition of HfC0.638N0.271, which is ~80 K higher than the highest value in a Hf–C binary system. Dominating mechanism of the N addition is believed to be unstable C–N and N–N bonds in liquid phase, which reduces liquid phase entropy and renders the liquid phase less stable. The improved melting point and less gas generation during oxidation by the addition of N provide a new routing to modify thermal protection materials for the hypersonic vehicles.
Dr. Lei Chen would thank for the supports by the National Natural Science Foundation of China (Nos. 52032002, 51972081, and U2130103), University Nursing Program for Young Scholars with Creative Talents in Heilongjiang Province (No. UNPYSCT-2020052), and Heilongjiang Touyan Team Program. This work was supported by Bohrium Cloud Platform of DP Technology.
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made.
The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.
To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.