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Electronic structure,bonding characteristics,and mechanical behaviors of a new family of Si-containing damage-tolerant mab phases M_(5)SiB_(2)(M=IVB-VIB transition metals)

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Journal of Advanced Ceramics 2022年第10期11卷 1626-1640页

作者： Na NI Hanchao ZHANG Yanchun ZHOU School of Mechanical Engineering Shanghai Jiao Tong UniversityShanghai 200240China Science and Technology on Advanced Functional Composite Laboratory Aerospace Research Institute of Materials&Processing TechnologyBeijing 100076China

mab phases are layered ternary compounds with alternative stacking of transition metal boride layers and group A element layers.Until now,most of the investigated mab phases are concentrated on compounds with Al as the A element layers.In this work,the family of M_(5)SiB_(2)(M=IVB-VIB transition metals)compounds with silicon as interlayers were investigated by density functional theory(DFT)methods as potential mab phases for high-temperature applications.Starting from the known Mo5SiB2,the electronic structure,bonding characteristics,and mechanical behaviors were systematically investigated and discussed.Although the composition of M_(5)SiB_(2) does not follow the general formula of experimentally reported(MB)_(2z)A_(x)(MB_(2))_(y)(z=1,2;x=1,2;y=0,1,2),their layered structure and anisotropic bonding characteristics are similar to other known mab phases,which justifies their classification as new members of this material class.As a result of the higher bulk modulus and lower shear modulus,Mo_(5)SiB_(2) has a Pugh’s ratio of 0.53,which is much lower than the common mab phases.It was found that the stability and mechanical properties of M_(5)SiB_(2) compounds depend on their valence electron concentrations(VECs),and an optimum VEC exists as the criteria for stability.The hypothesized Zr and Hf containing compounds,i.e.,Zr_(5)SiB_(2) and Hf_(5)SiB_(2),which are more interesting in terms of high-temperature oxidation/ablation resistance,were found to be unfortunately unstable.To cope with this problem,a new stable solid solution(Zr_(0.6)Mo_(0.4))_(5)SiB_(2) was designed based on VEC tuning to demonstrate a promising approach for developing new mab phases with desirable compositions.

关键词： borides mab phases density functional theory(DFT) thermodynamic stability electronic structure mechanical properties

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Cr5Si3B and Hf5Si3B:New mab phases with anisotropic electrical,mechanical properties and damage tolerance

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Journal of Materials Science & Technology 2018年第8期34卷 1441-1448页

作者： Yanchun Zhou Huimin Xiang Fu-Zhi Dai Zhihai Feng Science and Technology on Advanced Functional Composite Laboratory Aerospace Research Institute of Materials&Processing TechnologyNo.1 South Dahongmen RoadBeijing 100076China

Through a combination of electronic structure, chemical bonding and mechanical property investigations, anisotropic electrical and mechanical properties, and damage tolerant ability of mab phases CrsSi3 B and HfsSi3B are predicted. The anisotropic electrical conductivity is due to the anisotropic distribution of Cr in CrsSiaB and Hf in HfsSi3B, which mainly contribute to the electrical conductivity. The anisotropic mechanical properties are underpinned by the anisotropic chemical bonding within the crystal structures of CrsSi3B and HfsSi3B. The high stiffness is determined by the strong covalent-ionic Crl--B--Crl and Crl--Si bonds in CrsSi3B and the ionic-covalent Hfl--B--Hfl and Si--B bonds in HfsSi3B; while the low shear deformation resistance is attributed to the presence of metallic Cr--Cr, Hf--Hf and Si--Si bond. Based on the low Pugh＇s ratio, CrsSi3B and Hfs Si3B are predicted tolerant to damage. The possible cleavage plane is （0001） and the possible slip systems are 〈1 100〉1{11 20} and 〈11 20〉1{0001} for both CrsSi3B and HfsSi3B.

关键词： mab phases CrsSi3B and HfsSi3 BFirst-principles calculations Mechanical properties Chemical bonding

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Ultra-fast synthesis and thermodynamic analysis of MoAlB by self-propagating high-temperature combustion synthesis

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Journal of Advanced Ceramics 2023年第2期12卷 258-267页

作者： Hang YIN Xiaodong HE Guangping SONG Yongdong YU Yongting ZHENG Yuelei BAI National Key Laboratory of Science and Technology on Advanced Composites in Special Environments and Centre for Composite Materials and Structures Harbin Institute of TechnologyHarbin 150080China

MoAlB as a typical member of mab phases has attracted much-growing attention due to its unique properties.However,the low production of MoAlB powders limits its further development and potential applications.In the present work,the ultra-fast preparation of high-purity MoAlB powders in a few seconds is achieved by self-propagating high-temperature synthesis(SHS)using a raw powder mixture at an atomic ratio of Mo:Al:B=1:1.3:1.SHS reaction mechanism is obtained by analyzing the corresponding composition changes of starting materials.Furthermore,the thermodynamic prediction for the SHS reaction is consistent with the present experiments,where the preparation of MoAlB also conforms to two common self-propagating conditions of the SHS.The enthalpy vs.temperature curve shows that the adiabatic temperature of the reaction decreases with the amount of excuse Al increasing but increases when pre-heating the reactants.Also,this thermodynamic calculation provides a new idea for the preparation of other mab phases by the SHS.

关键词： MoAlB mab phases combustion synthesis thermodynamics self-propagating hightemperature synthesis(SHS)

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Theoretical prediction on the stability, electronic structure, room and elevated temperature properties of a new mab phase Mo2AlB2

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Journal of Materials Science & Technology 2019年第12期35卷 2926-2934页

作者： Yanchun Zhou Huimin Xiang Haiming Zhang Fu-Zhi Dai Science and Technofogy on Advanced Functional Composite Laboratory Aerospace Research institute of Maferids Processing Technofogy.No.1 South Dahongmen RoadBeijing 100076China School of Mechanical Electronic and Control EngineeringBeijing Jiaotong UniversityBeijing 100044China

Mo2AlB2 is a new mab phase that has been observed in thin foils of Mo Al B during TEM observation and in Na OH etched Mo Al B samples. However, the structural characteristics, chemical bonding and properties of this new compound have not been investigated. In this work, geometry optimized crystal structure of Mo2AlB2 is obtained and its stability, elastic and thermal dynamic properties are investigated. Mo2AlB2 is stable in Al lean conditions, which is consistent with the exiting experimental results. It is also gauged as a damage tolerant or quasi-ductile ceramic based on the low Pugh’s shear to bulk modulus ratio(G/B = 0.544) and positive Cauchy pressure in all three crystallographic directions, which is underpinned by the metallic bonding. Mo2AlB2 also exhibits high stiffness which is attributed to the strong B–B covalent bond chains within its crystal structure. Due to the anisotropic chemical bonding, Mo2AlB2 has anisotropic thermal expansion coefficients αa= 6.19 × 10^–6 K1, αb= 12.13 × 10^-6 K^–1, αc= 6.66 × 10^-6 K^–1,respectively, along a, b and c directions in the temperature range between 300 and 1500 K. The heat capacity from 300 to 1500 K can be described as Cp= 120.32 + 0.01648 T-2.597 × 10^6 T^-2(J·mol^–1·K^–1).The elastic constants decrease almost linearly with temperature. The elastic constants representing the resistance to principle deformation(c11, c22 and c33) decrease in faster rates than those representing shear deformation resistance(c44, c55 and c66). Correspondingly, bulk and Young’s modulus decrease in faster rates than shear modulus. In light of the structure-property relations of Mo2AlB2, it is suggested that future damage tolerant ceramics can be designed by putting stiff covalent bonding units into soft metallic bonding box to obtain both high stiffness and quasi-ductility.

关键词： mab phases Mo2AlB2 Damage tolerant ceramics Phase Stability Elastic properties Thermodynamic properties

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First demonstration of possible two-dimensional MBene CrB derived from mab phase Cr_2AlB_2

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Journal of Materials Science & Technology 2018年第11期34卷 2022-2026页

作者： Haiming Zhang Huimin Xiang Fu-zhi Dai Zhili Zhang Yanchun Zhou Science and Technology on Advanced Functional Composite Laboratory Aerospace Research Institute of Materials & Processing Technology School of Mechanical and Electrical Control Engineering Beijing Jiaotong University

In this communication, the possibility for the preparation of two-dimensional MBene CrB from mab phase Cr2AlB2 is demonstrated for the first time. Herein M is a transition metal, A is a group IIIAor IVA element and B is boron; mab phases are layered transition metal ternary borides, MBene is used to emphasize the loss of A group element from the parent mab phases and to highlight the 2 D nature. The possible 2 D CrB nano sheets are prepared by selectively etching out Al layers from Cr2AlB-2 by immersing the Cr2AlB2 powders in dilute HCl solution at room temperature. The as-prepared 2 D CrB nano sheets are examined using X-ray diffraction and scanning electron microscopy and energy dispersive X-ray spectroscopy（EDS）. In addition, different structure models are built to explain the observed phenomena.The discovery in this work opens a door to the synthesis of a large number of new 2 D MBenes from mab phases.

关键词： 2D CrB nano sheets MBene mab phases Exfoliation Transition metal borides

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