Deqiang Yin

Electronic property and bonding configuration at the TiN(111)/VN(111) interface

Multilayered TiN(111)/VN(111) coatings find many technological applications where the behaviors of their inside interfaces are known or suspected to influence functionalities in such an engineering surface system. Here, we demonstrate, by first-principles calculations on energetics and electronic structures of a total of 36 candidate interfaces, that the preferred geometries (i.e., that having the largest adhesion energy) are those that retain the interface structures as in either of the nitride bulks both atomically and electronically. Using several analytic methods, we have thoroughly characterized electronic states and determined that the interfacial bondings are mainly ionic, yet maintain a small amount of covalent character. The theoretical calculations presented provide insight into the complex electronic properties of the functional TiN/VN interface that could be difficult to obtain by experiment alone but which are practically important for further understanding and improvement of such a multilayered coating at the atomic scale.

Molecular dynamics simulation of the slip systems in VN

We calculate the generalized stacking fault (GSF) energies along different slip directions in various slip planes of VN, aimed to probe the mechanical properties of different slip systems of VN. We find that the 〈110〉 directions on various slip planes exhibit the lowest maximum GSF energies among the possible slip directions, and the sequence of the maximum GSF energies along the 〈110〉 directions on the possible slip planes is W{110} < W{111} < W{001}, implying that the sequence of the slip planes in VN is {110}, {111} and {001}. We also find that on the {111} planes, the slip can form two Shockley partial dislocations oriented by 〈112〉, resulting in a perfect dislocation on the 〈110〉 directions. The predicted sequence of the slip planes during indentation agrees with that assessed by the maximum GSF energies.

Atomic-scale observation of dynamical fluctuation and three-dimensional structure of gold clusters

Unravelling three-dimensional structures and dynamical fluctuation of metal nanoclusters is critical to understanding reaction process and the origin of catalytic activity in many heterogeneous catalytic systems. We obtain three-dimensional structures of ultra-small Au clusters by combining aberration-corrected scanning transmission electron microscopy, density functional theory calculations, and imaging simulations. The configurations of unique Au clusters are revealed at the atomic scale and the corresponding electronic states are given. The sequential observations reveal a transition of ultra-small Au clusters with about 25 atoms from a near-square to an elongated structure. We also find a transition from two dimensions to three dimensions for the Au clusters. The obtained three-dimensional geometry and associated electronic states help to clarify atomistic mechanism of shape- and number-dependent catalytic activities of Au clusters.

Sintering Thermodynamics of Fields Activated Microforming and Sintering Technology for Fabricated MnZn Ferrite Microparts

MnZn ferrites are widely used as core materials in electronic applications. However, few studies on fabricated MnZn ferrites microcomponents are available in this paper. To address this issue, a novel fields-activated microforming and sintering technology (micro-FAST) was introduced for the fabrication of MnZn ferrites microparts. The experimental results show that micro-FAST is an efficient process, which has lower energy consumption and little impact on the environment as a result of directly forming the component from loose powders. More interestingly, MnZn ferrite powders with a composition of Zn0.8Mn0.2Fe2O4(wt.%) can be sintered at low temperature without much compromise of the final quality of microparts formed by micro-FAST. To analyze the sintering mechanism, in this paper, the sintering thermodynamics of micro-FAST for the fabrication of Φ 1.0 mm × 1.0 mm sized cylindrical bulk ferrite has been studied. The results show that the sintering energy of micro-FAST for MnZn ferrite powder comes from three sources: 1) heat exchange with die and punches; 2) alternating electric field; and 3) alternating magnetic field. These results being in correspondence with the analytical results of computer simulation.

Study on plasma of micro-forming fields activated sintering technology

In order to study whether plasmas exist between powder particles during the densification of low-temperature and fast-forming of micro-forming fields activated sintering technology (Micro-FAST), pure copper powders were chosen purposely in this paper and the micrographs of particle surfaces were examined by high resolution transmission electron microscope (HRTEM). It is found that the oxide layers exist between the surfaces of copper powders before and after the sintering. Moreover, the stacking sequences of atoms at interfacial district (i.e. the joint section of two particles) are obviously different from those within the particles. It is concluded that there is no evidence of existence of plasmas among powder particles during the densification process of Micro-FAST, and the sintering densification mechanism of Micro-FAST is evidently different from that of spark plasma sintering.

Micro-sintering through a FAST process

As demands on miniature/micro-metal-products increase significantly, micro-metal-forming becomes an attractive option in the manufacturing of these products due to its advantageous characteristics for mass production. Forming is a particularly appropriate manufacturing technique for micro-parts, as often they have a complicated shape and machining would be time-consuming and produce low yield. To address this issue, a novel micro-forming technology, named as micro-fields-activated sintering technology (Micro-FAST, combining micro-forming and FAST), was introduced for the forming of micro-components. In Micro-FAST, loose powders were pressed and sintered to form micro-parts with coupled multifields activation, i.e., electrical field, stress field, and temperature field, with a Gleeble-1500D thermal simulation machine. The experimental results show that Micro-FAST is an efficient process, having lower energy consumption and little impact on the environment as a result of directly forming the component from loose powders.

Effect of soaking time on the preparation of porous NiTi alloy during fields-activated micro-sintering and forming technology

In this study, porous NiTi alloys have been successfully produced by fieldsactivated micro-sintering and forming technology under the pressure of 75 MPa at 1100◦C. The effects of soaking time on the porous NiTi alloys were investigated by analysing porosities, microstructures, and phase compositions of the produced alloys. The porosities of 41.2%, 38.8% and 47.2% are achieved at the soaking time of 2 min, 6 min and 10 min respectively. SEM examinations show that the pore size is varied with the soaking time and X-ray diffraction studies reveal that the main phases are NiTi, Ni3Ti and NiTi2.

Structure optimization and casting simulation of engine trestle based on CAE technology

Reasonable structure design is premised on making the product structure lightweight and green production, therefore through the ANAYS sofLare on the structural design and optimization can reduce the process of product development, and improve the efficiency of product design. ANSYS Workbench was used to analyze the conditions of static, dynamic and fatigue characteristics, the trestle structure parameter optimization, and realized the trestle structure optimization design. The simulation results have shown that the optimized trestle weight reduced about 60% compare to the original casting, reduced more than 20% compared with the original change plan. At the same time, the maximum stress value on focused regional reduced by 30% or more, which makes the structure more reasonable. Then the casting process of trestle optimization structure was simulated to verify the optimized parts production feasibility, and effectively predict the casting structure and casting process design flaws, for further optimization of casting process provides important reference by MAGMA software.