Key Engineering Materials Vol. 871

Abstract: γ-Fe/(Cr, Fe)₇C₃ lamellar eutectics reinforced the composite coating was deposited onto the 16Mn steel surface to enhance its surface hardness and wear resistance. The microstructure, phase composition, microhardness as well as wear resistance of the cladding coating were explored. Results indicated that the coating showed the dense and defect-free metallurgical bonding with the substrate and mainly consisted of (Cr, Fe)₇C₃, γ-Fe/(Cr, Fe)₇C₃ lamellar eutectic, B₄C and carbon fibers. (Cr, Fe)₇C₃, B₄C and carbon fibers were tightly embedded in the γ-Fe/(Cr, Fe)₇C₃ lamellar eutectics matrix. The microhardness and wear resistance of the coating compared with that of the substrate were highly improved by nearly 5 and 3 times, respectively.

Abstract: The phase composition and microstructure of ZrO₂ metering nozzle matrix doped with different content stabilizer were researched by XRD, SEM and EDS. Result showed that the content of cubic phase increased accompanied with monoclinic phase decreased after sintering, different content of stabilizer made phase transition not the same; After sintering in the solid solution formed by MgO and ZrO₂, with closer location to the MgO particles, substitution degree was more obvious, but the diffusion and solid solution state of the stabilizer were far from uniform.

Abstract: To optimize the structure of the automobile energy-absorbing box and obtain the energy-absorbing box structure with improved impact energy absorption property, and apply it to the structure of automobile energy absorption box, test piece of crystal lattice structure and polycrystalline structure of energy-absorbing box are designed via rapid prototyping technology in this study Four different crystal lattice structures of triangle, quadrangle, hexagon, and hollow lattice structure are designed respectively. And their mechanical properties, impact energy absorption properties, and impact properties are tested. The results show that the wall thickness of the four lattices differs greatly when the quality of all crystal lattice structures is 17.8g. The compressive strength and yield strength of the hollow crystal lattice structure test piece are the largest, reaching 51.1Mpa and 69.2Mpa respectively. The maximum compression modulus of the hexagonal lattice test piece is 1462.1, followed by the hollow crystal lattice structure test piece, whose compression modulus value is 1341. The minimum absorption energy of the hollow lattice structure energy-absorbing box test piece is 2847.99J. The minimum impact value of the hollow lattice structure energy-absorbing box test piece is 69.251KN, and the impact value of triangle structure energy-absorbing box test piece is 118.11 KN. The effective impact time of the drop weight test of the hollow lattice structure energy-absorbing box test piece is only 0.08s, the peak value of the impact acceleration is 28.96g, and the maximum load of the test piece is 26.95KN. According to the comprehensive indicators, the hollow lattice structure energy-absorbing box test piece designed based on rapid prototyping technology has improved the impact energy absorption property of the automobile energy-absorbing box.

Abstract: The properties and structure changes of SiC fiber in high temperature determine the service temperature of the reinforced ceramic matrix composites, so the properties of SiC fibers under high temperature are very important. The SiC-A and SiC-B fibers were treated at 1200, 1350 and 1600°C in Ar atmosphere. Then the tensile strength was measured, the microstructure and composition of the fibers were analyzed by SEM, EDS, XRD and AES. The results show that the tensile strength of SiC-A and SiC-B decrease slowly at 1200 and 1350°C, but decrease rapidly at 1600°C.

Abstract: With the discovery of high-temperature superconducting (HTS) tape and the improvement of the performance of the second-generation HTS tape, the application of superconductors in power system is gradually unfolding. There have been many demonstration projects at home and abroad. When the HTS tape is applied to the power cable, the mechanical external action of the cable winding, laying and installation operations, and the Ampere force when the current is applied are applied to it. Stress has an important influence on the critical current characteristic of the superconducting tape. In different application scenarios of the tape, different materials and thicknesses reinforcement layers can be chosen. In this paper, for the YBCO superconducting tapes with different reinforcement layers, a set of systems with critical current under tensile stress at cryogenic temperature is used to study the influence of tensile stress on the critical current of superconducting tape at low temperature. We analyze the influence of the structure of the superconducting tape on the characteristics of the tape and studied its degradation characteristics, which have guiding significance for the design and operation of the superconducting cable.

Abstract: To prepare a kind of Fe-Cu-based friction material with good friction performance and wear resistance, and apply it to the brake structure of automobile machinery, the powder metallurgy method is used to prepare the friction materials in the standard with 4% Ni, 4% Mo and 2% Sn as the auxiliary material, SiC, Al₂O₃, and zircon sand as the basic friction material, 8% graphite and 3% MoS₂ as the lubricating component. Meanwhile, 50% Fe and 20% Cu is used for the preparation of friction materials. The friction and wear resistance can be increased by increasing the carbon fiber content of 0-8% concentration of the material. The results show that the friction coefficient of the Fe-Cu-based friction material is relatively gentle after the addition of 2% carbon fiber, and the compactness peaks, reaching 93.3%. Its shear strength and impact strength peak, which are 37.42Mpa and 6.7J/cm² respectively. 4% carbon fiber material with a hardness of 120.2 HV is the hardest one, followed by 2% carbon fiber material with a hardness of 118.1 HV. Added with 2% carbon fiber, the abrasion amount of the friction-based material is 0.0027 g at room temperature and-0.0008 g at 400°C after 60 minutes respectively. With all indicators considered, the result shows that the friction performance and wear resistance of Fe-Cu-based friction materials can be increased by adding 2% carbon fiber during the preparation of basic friction materials.

Abstract: In this paper, the dry cutting performance of Al₂O₃/TiC-based ceramic composites with nanoCaF₂ was studied. Compared with the Al₂O₃/TiC ceramic tool, the Al₂O₃/TiC/CaF₂ ceramic tool has lower cutting force, cutting temperature and surface roughness when milling 40Cr hardened steel. Three cutting parameters of cutting speed, feed per tooth, and cutting depth were used to conduct orthogonal experiments to study its changing trend. Through testing of cutting force, cutting temperature and surface roughness, and by comparison with ceramic tools without nanosolid lubricant added, the order of influence of three cutting parameters on cutting force, cutting temperature and surface roughness was obtained. The experimental results showed that the cutting force, cutting temperature and surface roughness of Al₂O₃/TiC/CaF₂ ceramic tools containing nanoCaF₂ werebetter than those of Al₂O₃/TiC ceramic tools. The cutting force, the cutting temperature, and the surface roughness were respectively reduced by 16.5%, 25.8% and 43% compared to when no solid lubricant was added. In addition, after adding solid lubricant, the effect of cutting depth on cutting force was significantly reduced. The average friction coefficient of the tool rake surface was 31.1% lower than that of ceramic tools without solid lubricant. In order to explain this phenomenon, through scanning electron microscopy (SEM) scanning and energy spectroscopy (EDS) elemental analysis, the wear reduction mechanism of solid lubricants was analyzed, that is, during the cutting process, nanosolid lubricants precipitated and formed lubricating film on the rake surface of the tool to reduce the friction coefficient. This was also the main reason for reducing the cutting temperature.

Abstract: In the process of ceramic stereolithography, the polymerization process of acrylate is exothermic, resulting in changes to temperature of the slurry, which may affect the quality of green parts. In this work, the heat source input in simulation is based on the in-situ measurement of conversion rate and calculated polymerization exotherm. The simulation results showed that the different structures underwent a 1~3°C maximum temperature rise. A thermal infrared detector was used to capture the in-situ temperature changes in entire exposure surface for several structures during the photopolymerization process. The experimental data validated the simulation results and showed that the temperature change and distribution area in the process were related to the exposure structure. The discontinuous structure and the increase of structural boundary length could accelerate the thermal diffusion, thus reducing the heat concentration in the center. Polymerization rate rose marginally with the incident light intensity until at the intensity of 20 milliwatts. Besides, intensity had little effect on the temperature gradient from the center to the boundary of the exposure area. It is inferred that the additional temperature rise after the peak temperature is an indicator of the occurring of secondary photopolymerization during multilayer exposure. And for the same input energy, reducing the exposure intensity and increasing the exposure time to some extent may help improve the degree of secondary photopolymerization. This work provided valuable guidance for the study of the photopolymerization process and structural design of ceramic stereolithography.

Abstract: In this work, we use first principles DFT calculations, anharmonic phonon scatter theory and Boltzmann transport method, to predict a comprehensive study on the thermoelectric properties as electronic and phonon transport of layered LaSe₂ crystal. The flat-and-dispersive type band structure of LaSe₂ crystal offers a high power factor. In the other hand, low lattice thermal conductivity is revealed in LaSe₂ semiconductor, combined with its high power factor, the LaSe₂ crystal is considered a promising thermoelectric material. It is demonstrated that p-type LaSe₂ could be optimized to exhibit outstanding thermoelectric performance with a maximum ZT value of 1.41 at 1100K. Explored by density functional theory calculations, the high ZT value is due to its high Seebeck coefficient S, high electrical conductivity, and low lattice thermal conductivity .

Abstract: Diamond/aluminum matrix composite with high thermal conductivity is of great significance to solve the heat dissipation problem of large-scale integrated circuits and high-power components. This paper reviews the current research status of diamond/aluminum matrix composites, and analyzes the effects of the preparation and processing of the composites, the interface bonding between diamond and aluminum matrix, the reinforced diamond and matrix alloy elements on the properties of the composites.