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Thermal properties and high-temperature ablation of high-entropy (Ti_(0.25)V_(0.25)Zr_(0.25)Hf_(0.25))B_(2) coating on graphite substrate

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Journal of Advanced ceramics 2024年第8期13卷 1268-1281页

作者： Ana C.Feltrin Daniel Hedman Farid Akhtar Division of Materials Science Lulea University of TechnologyLulea 97187Sweden Center for Multidimensional Carbon Materials(CMCM) Institute for Basic Science(IBS)Ulsan 44919Republic of Korea

An entropy-stabilized multicomponent ultrahigh-temperature ceramic(UHTC)coating,(Ti_(0.25)V_(0.25)Zr_(0.25)Hf_(0.25))B_(2),on a graphite substrate was in-situ sintered by spark plasma sintering(SPs)from constituent transition metal diboride ***(Ti_(0.25)V_(0.25)Zr_(0.25)Hf_(0.25))B_(2) coating had a hardness of 31.2±2.1 GPa and resisted 36.9 GPa of stress before delamination,as observed at the *** temperature-dependent thermal properties of the multicomponent diboride(Ti_(0.25)V_(0.25)Zr_(0.25)Hf_(0.25))B_(2) were obtained by molecular dynamics(MD)simulations driven by a machine learning force field(MLFF)trained on density functional theory(DFT)*** thermal conductivity,density,heat capacity,and coefficient of thermal expansion obtained by the MD simulations were used in time-dependent thermal stress finite element model(FEM)*** low thermal conductivity(temperatures,and therefore,the coating was mechanically resistant to the thermal stress induced during *** experiments at 220℃ showed that the multicomponent diboride coating was resistant to thermal stresses with no visible cracking or *** ablation mechanisms were mechanical denudation and evaporation of B_(2)O_(5) and light V-Ti oxides,which caused a decrease in the mass and thickness of the coating and resulted in mass and linear ablation rates of-0.51 mg·s^(-1) and -1.38μm·s^(-1),respectively,after 60 *** findings demonstrated the thermal and mechanical stability of multicomponent entropy-stabilized diborides as coatings for carbon materials in engineering components under extreme environments.

关键词： entropy-stabilized diborides ultrahigh temperature ceramics molecular dynamics(MD)simulations density functional theory(DFT) ablation properties

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Theoretical predictions and experimental verification on the phase stability of enthalpy-stabilized HE TMREB_(2)s

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Journal of Materials Science & Technology 2022年第26期121卷 154-162页

作者： Ze Zhang Shizhen Zhu Fu-Zhi Dai Huimin Xiang Yanbo Liu Ling Liu Zhuang Ma Shijiang Wu Fei Liu Kuang Sun Yanchun Zhou School of Materials Science and Engineering Beijing Institute of TechnologyBeijing 100081China Science and Technology on Advanced Functional Composite Laboratory Aerospace Research Institute of Materials and Processing TechnologyBeijing 100076China National Key Laboratory of Science and Technology on Materials Under Shock and Impact Beijing 100081China Beijing Institute of Technology Chongqing Innovation Center Chongqing 401120China Yangtze Delta Region Academy of Beijing Institute of Technology Jiaxing 314019China Zibo Firststar New Material Incorporated Co. Ltd.Zibo 255000China Shanghai Chenhua Science and Technology Corporation Ltd. Shanghai 201804China

Transition metal diborides(TMB_(2)s)are the materials of choice in extreme environments due to their excellent thermal and chemical ***,the degradation of oxidation resistance of TMB_(2)s at elevated temperature still hinders their *** cope with this challenge,it is effective to incorporate rare earth elements to form high-entropy transition and rare-earth metal diborides(HE TMREBs).To obtain thermodynamically stable single-phase structures for HE TMREB_(2)s,a“16×16 mixed enthalpy matrix”is constructed using first-principles calculations to predict the single-phase formation ability of120 two-component diborides(TCBs).Through the use of the“16×16 mixed enthalpy matrix”of TCBs,specific combinations of TMB_(2)s and REB_(2)s that are most likely to form single-phase HE TMREB_(2)s are ***,based on the energy distribution of the local mixing enthalpies of all possible configurations,the enthalpy and entropy descriptors of HE TMREB_(2)s(RE=Sc,Lu,Tm,Er,Ho and Dy)are *** is found that the mixing enthalpy plays a critical role in the stability of the single-phase HE TMREB_(2)s,i.e.,HE TMREB_(2)s are enthalpy-stabilized *** experimental results further confirm that enthalpy dominates the thermodynamic domain and drives the stability of REB_(2)s in HE TMREB_(2)*** study validates that enthalpy-stabilized HE TMREB_(2)s can further expand the compositional space of ultrahigh temperature ceramics(UHTCs)and is expected to further improve the oxidation resistance and high temperature properties of UHTCs.

关键词： High-entropy ceramics ultrahigh temperature ceramics First-principles calculation Mixing enthalpy Transition and rare earth metal diborides

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