Bin Wen

Body‐Centered Tetragonal C16: A Novel Topological Node‐Line Semimetallic Carbon Composed of Tetrarings

The present work not only predicts the existence of 3D topological semimetallic carbon allotropes composed of tetrarings, but also provides a likely crystalline structure for the unknown phase produced in the detonation soot.

Stress-Induced Grain Growth in an Ultra-Fine Grained Al Alloy

This paper reports on a study of the stress-induced grain growth phenomenon in the presence of second-phase particles and solutes segregated at grain boundaries (GBs) during high-temperature deformation of an ultra-fine grained (UFG) Al alloy synthesized via the consolidation of mechanically milled powders. Our results show that grain growth was essentially inhibited during annealing at 673xa0K (400xa0°C) in the absence of an externally applied stress, whereas in contrast, grain growth was enhanced by a factor of approximately 2.7 during extrusion at 673xa0K (400xa0°C). These results suggest that significant grain growth during hot extrusion was attributable to the externally applied stresses stemming from the state of stress imposed during extrusion and that the externally applied stresses can overcome the resistance forces generated by second-phase particles and solutes segregated at GBs. The mechanisms underlying stress-induced grain growth were identified as GB migration and grain rotation, which were accompanied by dynamic recovery and possible geometric dynamic recrystallization, while discontinuous dynamic recrystallization did not appear to be operative.

{111}-specific twinning structures in nonstoichiometric ZrC0.6 with ordered carbon vacancies

Twinning structures in ordered nonstoichiometric ZrC0.6 have been investigated experimentally and theoretically. Via transmission electron microscopy and selected area electron diffraction measurements, {111}-specific twins have been observed. Interestingly, two special types of twinning interfaces, i.e. (111)C and (111)Zr interfaces, are recognized to be formed as a result of the presence of ordered carbon vacancies. In contrast to the high stacking fault energy for twinning formation in stoichiometric ZrC, first-principles calculations indicate that the presence of ordered carbon vacancies leads to a great reduction in the twinning interfacial energy, thus favouring the stabilization of twinning structures in the ordered ZrC0.6.

Engineering Bulk, Layered, Multicomponent Nanostructures with High Energy Density.

The precise control of individual components in multicomponent nanostructures is crucial to realizing their fascinating functionalities for applications in electronics, energy-conversion devices, and biotechnologies. However, this control remains particularly challenging for bulk, multicomponent nanomaterials because the desired structures of the constitute components often conflict. Herein, a strategy is reported for simultaneously controlling the structural properties of the constituent components in bulk multicomponent nanostructures through layered structural design. The power of this approach is illustrated by generating the desired structures of each constituent in a bulk multicomponent nanomaterial (SmCo + FeCo)/NdFeB, which cannot be attained with existing methods. The resulting nanostructure exhibits a record high energy density (31 MGOe) for this class of bulk nanocomposites composed of both hard and soft magnetic materials, with the soft magnetic fraction exceeding 20 wt%. It is anticipated that other properties beyond magnetism, such as the thermoelectric and mechanical properties, can also be tuned by engineering such layered architectures.

Mechanical and thermal properties of γ-Mg2SiO4 under high temperature and high pressure conditions such as in mantle: A first principles study

γ-Mg2SiO4 is an important mineral in mantle, and our knowledge on its mechanical and thermal properties is critical for many areas of geological sciences. In this work, the crystal structure of γ-Mg2SiO4 under high temperature and high pressure conditions is optimized by using the GOMASC method, and the total energy, thermal expansion coefficients, and elastic constants at different temperature and pressure conditions are obtained. On the basis of phonon spectrum, group velocity, phase velocity, Grüneisen parameter, and thermal conductivity are calculated for γ-Mg2SiO4 under high temperature and high pressure conditions. These calculated results can provide an important reference for geological research.

Role of plastic deformation in tailoring ultrafine microstructure in nanotwinned diamond for enhanced hardness

Nanotwinned diamond (nt-diamond), which demonstrates unprecedented hardness and stability, is synthesized through the martensitic transformation of onion carbons at high pressure and high temperature (HPHT). Its hardness and stability increase with decreasing twin thickness at the nanoscale. However, the formation mechanism of nanotwinning substructures within diamond nanograins is not well established. Here, we characterize the nanotwins in nt-diamonds synthesized under different HPHT conditions. Our observation shows that the nanotwin thickness reaches a minimum at ~ 20 GPa, below which phase-transformation twins and deformation twins coexist. Then, we use the density-functional-based tight-binding method and kinetic dislocation theory to investigate the subsequent plastic deformation mechanism in these pre-existing phase-transformation diamond twins. Our results suggest that pressure-dependent conversion of the plastic deformation mechanism occurs at a critical synthetic pressure for nt-diamond, which explains the existence of the minimum twin thickness. Our findings provide guidance on optimizing the synthetic conditions for fabricating nt-diamond with higher hardness and stability.摘要在高温高压条件下以洋葱碳为原料合成的纳米孪晶金刚石具有前所未有的硬度和稳定性, 且二者随纳米孪晶厚度的减小而提高. 目前为止, 在金刚石纳米晶中纳米孪晶的形成机制尚不明确. 本研究通过分析在不同条件下合成的纳米孪晶金刚石块材中的孪晶厚度, 发现在合成压力约为20 GPa时孪晶厚度达到一个极小值(~5 nm). TEM结果表明在合成压力低于20 GPa时, 纳米孪晶金刚石中同时存在因马氏体相变而形成的相变孪晶和塑性形变所导致的形变孪晶. 针对马氏体相变后形成的相变孪晶内部塑性变形, 基于密度泛函理论的紧束缚方法和位错运动学理论的分析表明: 纳米孪晶金刚石的塑性变形存在一个依赖于压力的机制转变, 而机制转变的临界压力能够解释孪晶厚度随压力变化时出现的极小值. 本研究对通过优化合成条件制备出更高硬度和稳定性的纳米孪晶金刚石具有指导意义.

Erratum to: Stress-Induced Grain Growth in an Ultra-Fine Grained Al Alloy

This paper reports on a study of the stress-induced grain growth phenomenon in the presence of second-phase particles and solutes segregated at grain boundaries (GBs) during high-temperature deformation of an ultra-fine grained (UFG) Al alloy synthesized via the consolidation of mechanically milled powders. Our results show that grain growth was essentially inhibited during annealing at 673xa0K (400xa0°C) in the absence of an externally applied stress, whereas in contrast, grain growth was enhanced by a factor of approximately 2.7 during extrusion at 673xa0K (400xa0°C). These results suggest that significant grain growth during hot extrusion was attributable to the externally applied stresses stemming from the state of stress imposed during extrusion and that the externally applied stresses can overcome the resistance forces generated by second-phase particles and solutes segregated at GBs. The mechanisms underlying stress-induced grain growth were identified as GB migration and grain rotation, which were accompanied by dynamic recovery and possible geometric dynamic recrystallization, while discontinuous dynamic recrystallization did not appear to be operative.

Dislocation behaviors in nanotwinned diamond

The unprecedented hardness of nt-diamond originates from high lattice frictional stress and high athermal stress. Experimental results (Huang et al.) indicated that nanotwinned diamond (nt-diamond) has unprecedented hardness, whose physical mechanism has remained elusive. In this report, we categorize interaction modes between dislocations and twin planes in nt-diamond and calculate the associated reaction heat, activation energies, and barrier strength using molecular dynamics. On the basis of the Sachs model, twin thickness dependence of nt-diamond hardness is evaluated, which is in good agreement with the experimental data. We show that two factors contribute to the unusually high hardness of nt-diamond: high lattice frictional stress by the nature of carbon bonding in diamond and high athermal stress due to the Hall-Petch effect. Both factors stem from the low activation volumes and high activation energy for dislocation nucleation and propagation in diamond twin planes. This work provides new insights into hardening mechanisms in nt-diamond and will be helpful for developing new superhard materials in the future.