Temperature and face dependent copper–graphene interactions

The interaction between graphene and metals represents an important issue for the large-area preparation of graphene, graphene transfer and the contact quality in graphene devices. We demonstrate a simple method for estimating and manipulating the level of interaction between graphene and copper single crystals through heat treatment, at temperatures from 298 K to 1073 K. We performed in-situ Raman spectroscopy showing Cu face-specific behavior of the overlying graphene during the heat treatment. On Cu(1 1 1) the interaction is consistent with theoretical predictions and remains stable, whereas on Cu(1 0 0) and Cu(1 1 0), the initially very weak interaction and charge transfer can be tuned by heating. Our results also suggest that graphene grown on Cu(1 0 0) and Cu(1 1 0) is detached from the copper substrate, thereby possibly enabling an easier graphene transfer process as compared to Cu(1 1 1).     

镁合金轮椅小轮轴套焊接结构改进

研究了镁合金轮椅小轮轴套焊接部位的结构,改变了焊道的部位和方向,大大降低了焊接部位应力集中,有效地提高了焊接部位的疲劳强度。结果表明:焊道长度与疲劳性能有一定的关系,当焊道长度大于25 mm时,其疲劳寿命可达21万次以上,根据GB/T13800-2009标准测试满足轮椅的使用要求。     

Effect of Fe2O3 doping on color and mechanical properties of dental 3Y-TZP ceramics fabricated by stereolithography-based additive manufacturing

In this study, iron(III) oxide (Fe₂O₃)-doped zirconia (3Y-TZP) ceramics with desirable mechanical and color properties for dental restorations were fabricated by stereolithography-based additive manufacturing. Six zirconia ceramic paste specimens with high solid loading (58 vol%) and reasonably low viscosity were prepared according to doped content of Fe₂O₃ (0–0.14 wt%). Zirconia ceramics were fabricated using commercial stereolithography three-dimensional printer and sintered at 1500 °C for 4 h to obtain final dense parts with a relative density of above 99%. Effects of Fe₂O₃ doping on microstructure, mechanical properties, and color of 3Y-TZP ceramics were investigated. Results indicate that Fe₂O₃ exhibited little effect on the shrinkage and density of colored ceramics compared to uncolored ceramics. Average grain size of 3Y-TZP ceramics sintered at 1500 °C increased with increasing content of Fe₂O₃. X-ray diffraction analysis showed that tetragonal phase was dominant phase structure of white and colored 3Y-TZP ceramics, and monoclinic phase increased with increasing Fe₂O₃ content. Compared to uncolored specimens, Fe₂O₃ exhibited negative effects on three-point flexural strength (mean > 879.70 MPa), Vickers hardness (mean > 12.14 GPa), and indentation fracture toughness (mean > 4.23 MPa m^1/2) of the colored specimens. With the increase in the content of Fe₂O₃ from 0 to 0.14 wt%, L* (black–white index) value decreased from 83.39 to 79.54, a* (green–red index) value increased from −2.28 to −0.74, and b* (blue–yellow index) value increased from 1.15 to 17.94. Chromaticity (L*, a*, b*) fell within the range of natural tooth color, indicating that it is suitable for dental application because of its color compatibility with natural teeth. In addition, the transmittance slightly decreased with increasing Fe₂O₃ content. Thus, Fe₂O₃-doped 3Y-TZP ceramics can be used as potential candidates for aesthetic dental restoration materials.     

Improvement in fracture strength in electrically conductive AlN ceramics with high thermal conductivity

It is possible to impart electrical conductivity to insulating aluminum nitride (AlN) ceramics by precipitating a yttrium oxycarbide grain boundary phase with electrical conductivity. However, previously, sintering at high temperature was required to increase the electrical conductivity through the transformation of the grain boundary phase from yttrium aluminum oxide (Al₂Y₄O₉) to rare-earth oxycarbide. As a result, the increase in electrical conductivity was accompanied with a considerable decrease in the fracture strength due to grain growth of AlN. In this study, sintering temperature and additive compositions were investigated to maintain the high strength of electrically conductive AlN without losing the high thermal conductivity.     

Characterization of metal hydrides for thermal applications in vehicles below 0 °C

Metal hydrides promise great potential for thermal applications in vehicles due to their fast reaction rates even at low temperature. However, almost no detailed data is known in literature about thermochemical equilibria and reaction rates of metal hydrides below 0 °C, which, though, is crucial for the low working temperature levels in vehicle applications.Therefore, this work presents a precise experimental set-up to measure characteristics of metal hydrides in the temperature range of −30 to 200 °C and a pressure range of 0.1 mbar–100 bar. LaNi_4.85Al_0.15 and Hydralloy C5 were characterized. The first pressure concentration-isotherms for both materials below 0 °C are published. LaNi_4.85Al_0.15 shows an equilibrium pressure down to 55 mbar for desorption and 120 mbar for absorption at mid-plateau and −20 °C. C5 reacts between 580 mbar for desorption and 1.6 bar for absorption at −30 °C at mid-plateau.For LaNi_4.85Al_0.15, additionally reaction rate coefficients down to −20 °C were measured and compared to values of LaNi₅ for the effect of Al-substitution. The reaction rate coefficient of LaNi_4.85Al_0.15 at −20 °C is 0.0018 s⁻¹. The obtained data is discussed against the background of preheating applications in fuel cell and conventional vehicles.     

Characteristics of powder metallurgy pure titanium matrix composite reinforced with multi-wall carbon nanotubes

By using pure titanium powder coated with un-bundled multi-wall carbon nanotubes (MWCNTs) via wet process, powder metallurgy (P/M) titanium matrix composite (TMC) reinforced with the CNTs was prepared by spark plasma sintering (SPS) and subsequently hot extrusion process. The microstructure and mechanical properties of P/M pure titanium and reinforced with CNTs were evaluated. The distribution of CNTs and in situ formed titanium carbide (TiC) compounds during sintering was investigated by optical and scanning electron microscopy (SEM) equipped with EDS analyzer. The mechanical properties of TMC were significantly improved by the additive of CNTs. For example, when employing the pure titanium composite powder coated with CNTs of 0.35 mass%, the increase of tensile strength and yield stress of the extruded TMC was 157 MPa and 169 MPa, respectively, compared to those of extruded titanium materials with no CNT additive. Fractured surfaces of tensile specimens were analyzed by SEM, and the uniform distribution of CNTs and TiC particles, being effective for the dispersion strengthening, at the surface of the TMC were obviously observed.     

Tensile properties of carbon nanotube reinforced aluminum nanocomposite fabricated by plasma spray forming

Uniaxial tensile tests were performed on plasma spray formed (PSF) Al–Si alloy reinforced with multiwalled carbon nanotubes (MWCNTs). The addition of CNTs leads to 78% increase in the elastic modulus of the composite. There was a marginal increase in the tensile strength of CNT reinforced composite with degradation in strain to failure by 46%. The computed critical pullout length of CNTs ranges from 2.1 to 19.7 μm which is higher than the experimental length of CNT, leading to relatively poor load transfer and low tensile strength of PSF nanocomposites. Fracture surface validates that tensile fracture is governed strongly by the constitutive hierarchical microstructure of the plasma sprayed Al–CNT nanocomposite. The fracture path in Al–CNT nanocomposite occurs in Al–Si matrix adjacent to SiC layer on CNT surface.     

Powder metallurgy Ti–TiC metal matrix composites prepared by in situ reactive processing of Ti-VGCFs system

Titanium metal matrix composites (TMCs) were fabricated via powder metallurgy (P/M) and hot extrusion. Planetary ball milling (PBM) was employed to disperse 0.4–1.0 wt% multiwall carbon nanotubes (VGCFs) with pure Ti powder. The fragmented VGCFs were found dispersing homogenously on the flaked Ti particles surface after PBMed for 24 h. The powder mixture was consolidated at 1073 K by the spark plasma sintering (SPS) process. Hot extrusion was performed at 1273 K with an extrusion ratio of 37:1. The microstructures and mechanical properties of the extruded Ti-VGCFs composites were investigated to evaluate the reactive processing of Ti-VGCFs system. The extruded Ti-VGCFs composites, with a 1.0 wt% VGCFs additive dispersed by PBM, exhibited an excellent tensile strength of 1182 MPa in 0.2% YS and 1179 MPa in UTS, which demonstrated a 143.6% and 80.7% increase compared to these of the extruded pure Ti, respectively. The strengthening mechanism was investigated and elucidated that the mechanical strength was attributed to the grain refinement and dispersion strengthening of the homogenously dispersed, in situ formed TiC particulates, as well as a solid solution strengthening of the carbon, oxygen and nitrogen elements in the Ti matrix.