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In this paper, diamond microstructures were patterned over silicon/silicon dioxide substrate using the processes combined with bulk or surface micromachining, selective growth of diamond and plasma etching technique. Polycrystalline diamond films were prepared using microwave plasma enhanced chemical vapour deposition (MW-PECVD) and a gas mixture of hydrogen and methane. Two types of techniques for precise patterning of diamond microstructures were investigated in this paper. The first one was to selectively grow diamond films in the desired region by pre-depositing a Pt interlayer on silicon dioxide layer. The second one was to selectively etch the deposited diamond film in oxygen/argon plasma under an Al mask. Different microstructures, e.g., microgear, microrotor, comb drive structure, etc. were successfully fabricated. [Copyright &y& Elsevier]

• Direct ink writing combined with acoustofluidics enhances material control. • Organizing microparticles in flowing multiphase bioink. • Creating patterned and interconnected porous microstructures in 3D scaffolds. • Fibroblasts exhibit patterned distribution following the scaffold's microstructure. Vascular scaffolds with well-organized pore characteristics are crucial for promoting infiltration, adhesion, growth, tissue-specific arrangement, and substance-exchanges of biological cells. However, their controllable fabrication is extremely challenging, especially for those with specially designed three-dimensional (3D) tubular and porous microstructures. In this paper, a new methodology based on acoustofluidics-assisted direct ink writing (DIW) technique is developed to fabricate vascular scaffolds with controlled porosity distributions and well-defined porous microstructures. Calcium carbonate (CaCO 3) particles and alginate are uniformly mixed as the printing ink, which is printed along a rotating rod to form a vessel-like structure. Distributions of these CaCO 3 particles in the printed structure are precisely controlled using bulk acoustic waves. The particles within the vessel-like structure are dissolved in situ using hydrochloric acid, resulting in the formation of 3D vascular scaffolds with intrinsically patterned porous microstructures. The scaffolds printed by the acoustofluidics-assisted DIW method exhibit a 69% improvement in pore connectivity compared to conventional 3D-printed scaffolds. Fibroblast cells are successfully seeded onto these scaffolds, achieving distinctive distributions along the patterned porous microstructures. This innovative methodology, with its excellent microfabrication capabilities, holds great promise for applications in tissue engineering, drug release, composite formation, microfluidic chips, and biosensors. [ABSTRACT FROM AUTHOR]

Nanocrystalline TiN has been imbedded in amorphous silicon nitride matrix to form a super hard nanocomposite thin film (nc-TiN/a-SiNx) via magnetron sputtering. Adjusting Ti and Si3N4 target power ratio altered film composition, size, amount and distribution of the nc-TiN phase. At a Ti target power density of 5.5 W cm−2, the Ti to Si3N4 target power ratio should be greater than unity in order for nc-TiN to form, otherwise, Ti will dissolve in amorphous SiNx. The relationship between the film hardness and the crystallite size show Hall–Petch and anti-Hall–Petch relationship. A ‘scratch crack propagation resistance’ parameter, or CPRs=Lc1(Lc2−Lc1), has been proposed to approximate thin film toughness from the critical load data easily obtained from a scratch adhesion test. [Copyright &y& Elsevier]

Abstract Tungsten-copper (W-Cu) composites are used as high temperature frictional materials under special service conditions for electromagnetic gun rail and precision guide for rolled pieces due to their good ablation resistance and electrical conductivity. However, they have poor wear resistance at elevated temperatures. In this paper, surface carburization method was applied on the W-20 wt%Cu composite to investigate the mechanisms of carburization and its effects on the high temperature friction behavior of composite. Carburization process has been done at a temperature of 1100 °C for 30 h. The obtained results showed that carburizing at 1100 °C with a dwelling time of 30 h resulted into formation of a carburized layer and a dense intermediate sub-layer on the substrate. Also, the surface carburized layer with a thickness of about 70 μm composed of mixed phases of graphite, WC and W 2 C. The hardness of carburized layer (~HV454) was significantly higher than that of substrate (HV223). Also, bending strength of the carburized W-Cu composites has been significantly improved, although their electrical conductivity and tensile strength was decreased slightly. The carburization mechanism of the W-Cu composites was found to be dominant by carbon atom diffusion through reaction with W atoms and formation of surface liquid copper, which promoted migration and diffusion of tungsten and carbon at high temperatures. Average coefficients of friction and wear rate of carburized W-Cu composites are all lower than these of un-carburized W-Cu composites owing to the presence of surface carburized layer. Also, formation of CuWO 4 at high temperatures reduced the friction and wear resistance of the W-Cu composites. Highlights • First report on carburization of W-Cu composite for high temperature wear resistance • Carburization is dominant by C/W diffusion through reaction and surface liquid Cu. • The hardness of carburized layer (~HV454) was the double of substrate (HV223). • Formation of CuWO 4 is key reason to reduce wear at high temperatures. [ABSTRACT FROM AUTHOR]

Titanium matrix composites synthesized using powder metallurgy methods have attracted significant attention due to their extraordinary mechanical properties. In this study, cost-effective and high-performance TiC/Ti-6Al-4 V matrix composites were synthesized and characterized using a combined elemental powder mixing and spark plasma sintering method. Studies on the effect of graphene nanoplate (GNP) content on microstructures of Ti-6Al-4 V matrix composites showed typical Widmanstatten structures without apparent pores and microcracks. The grain size of composites was decreased significantly with the increase of GNP content, mainly due to the pinning effect of in-situ generated TiC particles at grain boundaries, which limited the rapid grain growth of the matrix. Mechanical test results showed that their yield strength and ultimate tensile strength were 889.0 MPa and 988.3 MPa, respectively, and their total fracture elongation was maintained at ∼14.2 %. GNPs/Ti-6Al-4 V exhibited superior strength (e.g., yield and ultimate tensile strength of 1028.4 and 1121.6 MPa, which are 14.4 % and 13.5 % higher than those of the matrix) and maintained a good ductility of ∼ 9.8 % with only 0.1 wt% GNP addition. Carbon nanomaterial (such as graphene nanoplates) induced the precipitation of needle-like nano-secondary phases in trigeminal grain boundary β phases, which strengthened the β-Ti soft phase. The reinforced strength of the composite is mainly attributed to the grain refinement, secondary α phases precipitation strength and dislocations strengthening. This work provides a new methodology for fabrication of high-performance titanium matrix composites (TMCs) combination blended elemental powder metallurgy (BEPM) and sintering technology. • BEPM and SPS were used to in-situ synthesize TiC/Ti-6Al-4 V composites. • GNPs induce precipitation α" in trigeminal grain boundary β, reinforcing β-Ti phase. • YS of composites are 1028.4 MPa, increased by 15.7 % compared to Ti-6Al-4 V alloy. • Strengthen mechanisms are grain refinement, α" precipitation and dislocations strengthening. [ABSTRACT FROM AUTHOR]

CuW composites were synthesized using an equal channel angular pressing (ECAP) technique. Microstructural evolution during sintering process was investigated using both optical microscopy and transmission electron microscopy (TEM), and their deformation mechanisms were studied using finite element analysis (FEA). Results showed severe plastic deformation of the CuW composites and effective refinement of W grains after the ECAP process. TEM observation revealed that the ECAP process resulted in lamellar bands with high densities dislocations inside the composites. Effects of extrusion temperature and extrusion angles on stress-strain relationship and sizes of deformation zones after the ECAP process were investigated both theoretically and experimentally. When the extrusion angle was 90°, a maximum equivalent stress of ~1001 MPa was obtained when the extrusion test was done at room temperature of 22 °C, and this value was lower than compression strength of the CuW composites (1105.43 MPa). The maximum equivalent strains were varied between 0.5 and 0.7. However, when the extrusion temperature was increased to 550 °C and further to 900 °C, the maximum equivalent stresses were decreased sharply, with readings of 311 MPa and 68 MPa, respectively. When the extrusion angle was increased to 135°, the maximum equivalent stresses were found to be 716.9 MPa, 208 MPa, and 32 MPa for the samples extruded at temperatures of 22 °C, 550 °C and 900 °C, respectively. Simultaneously, the maximum equivalent strains were decreased to 0.2–0.4. Furthermore, results showed that the maximum equivalent stress was located on the sample's external surface and the stress values were gradually decreased from the surface to the center of samples, and the magnitudes of plastic deformation zones at the surface were much larger than those at the central part of the sintered samples. FEA simulation results were in good agreements with experimentally measured ones. [ABSTRACT FROM AUTHOR]

W70Cu30(W-30 wt.% Cu) alloys were fabricated using cold pressing and infiltration sintering methods from two types of powders, i.e., mixed copper-tungsten (M-Cu-W) powders and our newly developed copper-coated tungsten composite (Cu@W) powders. Microstructure, mechanical and arc-ablation properties of the W70Cu30 alloys were investigated, and the mechanism of enhanced physical/mechanical properties and arc-erosion resistance of the W70Cu30 alloys was discussed. For the W70Cu30 alloys prepared using the Cu@W powders, their physical properties, including hardness, electrical conductivity and relative density were much better than those prepared from the M-Cu-W powders. The W70Cu30 alloys fabricated from the Cu@W powders were free of cracks, and showed homogenous distributions of W and Cu network structures. Whereas for the alloys prepared from the M-Cu-W powders, segregation of Cu was observed and the segregation size was about 40–100 μm. Characterization of arc-erosion morphologies of the W70Cu30 alloys prepared with the Cu@W powders revealed the occurrence of evaporation of Cu phase; whereas that of W70Cu30 alloys prepared with the M-Cu-W powders revealed the occurrence of the sputtering of Cu. After arc breakdown for 200 times, mass loss of alloys made using the mixed powders was twice as much as those made using the coated composite powders. Based on the experimental results and theoretical analysis, an arc breakdown mechanism of the WCu-C alloys using the composite powders was proposed which is attributed to the formation of a homogeneous Cu-Cu network structure to uniformly disperse arc energy and dissipate the generated heat, thus prolonging the service life of the WCu alloy contacts. [ABSTRACT FROM AUTHOR]

To solve critical issues of premature failure for copper tungsten (CuW) based electrical contacts during arc erosion at the moment of arc breakdown, we proposed a new strategy of using metal doped reduced graphene oxides (rGOs) and in-situ formed tungsten carbides to inhibit movements of cathode spots during the arc ablation process. CuW composites were reinforced with Cu modified rGO nanopowders (i.e. Cu@rGO) using combined processes of chemical co-reduction, ball milling and spark plasms sintering (SPS). Effects of Cu@rGO addition on microstructure, arc erosion resistance and arc ablation resistance of the CuW composites were systematically investigated. Results showed that tungsten carbides with irregular shapes were formed through in-situ reactions of rGO and tungsten during the SPS process. Arc erosion resistance of CuW composites was significantly improved owing to introduction of nanostructured Cu@rGO. Compared with those of CuW composites, the ablation areas of Cu@rGO/CuW ones were much smaller and the ablation craters were shallower, and the average strengths of dielectric vacuum breakdowns of the CuW composites with 3 wt% Cu@rGO were increased by 28.9%. The arc breakdown mechanisms of Cu@rGO/CuW composites were identified as: (1) The nanostructured Cu@rGO increases the viscosity of molten metal Cu, thus inhibiting its fast flow and splashing; (2) Lower work functions of carbon (i.e. rGO) and tungsten carbide restrain the electron emissions during arc breakdown; and (3) The tungsten carbides with their good stability and high melting point shorten the solidification time of molten copper liquid and extend the service life time of the Cu@rGO/CuW composites. • Introduced nanostructured Cu@rGO into CuW improve effectively dispersion effect. • Cu@rGO/CuW composites with smaller ablation area and shallower ablation craters. • Average arc breakdown strength of 3wt%Cu@rGO/CuW composites increased by 28.9%. • Arc breakdown mechanism were attributed to increasing of the viscosity of molten Cu, lower work functions of second phases. • Provides a new thought of enhanced arc erosion resistance of CuW with graphene decorated with metal nanoparticles. [ABSTRACT FROM AUTHOR]

H 2 S gas sensor based on α-Fe 2 O 3 nanoparticles was fabricated by post-thermal annealing of Fe 3 O 4 precursor which was synthesized using a facile hydrothermal route. The characteristic techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were adopted to characterize the chemical composition and microstructure of the obtained samples. Gas-sensing performance of the sensor was investigated at different operation temperatures from 100 °C to 400 °C. Results showed that the sensor exhibited the best sensitivity, reproducibility and long-term stability for detecting H 2 S gas at an operating temperature of 300 °C. The detection limit towards H 2 S gas was 0.05 ppm, and the response time and recovery time was 30 s and 5 s, respectively. In addition, sensing mechanism of the sensor towards H 2 S was discussed. [ABSTRACT FROM AUTHOR]

Abstract: Excellent thermal shock resistance is required for thermal protection coatings experiencing high/low temperature cycles. In this paper, the pure ceria oxide coatings were deposited by electron beam physical vapor technique at different power densities. The grain orientation, morphology, hardness and thermal cycling oxidation behavior of CeO2 coatings were systematically studied. The deposition power density has remarkable influence on the preferred crystal orientation and morphology of the coatings. The heating–cooling test cycles from 1000°C to room temperature indicate that the CeO2 coatings with the columnar structure show excellent thermal shock resistance. The hardness of the CeO2 coating varies with thermal cycling. [Copyright &y& Elsevier]

Zirconium pentatelluride (ZrTe 5) single crystal has recently received significant attention because of its quantum electronic transport properties and is regarded as a promising candidate for low-temperature thermoelectric cooling and spintronic applications. However, single crystal of ZrTe 5 has generally small sizes and can only be produced in small quantities using a complicated process, whereas ZrTe 5 polycrystals are easily produced and their properties are easily adjusted. In this study, we focus on the magneto-transport properties at low temperatures of nanocomposites of ZrTe 5 produced using both hand-milling and ball-milling processes to investigate the impact of the microstructure. The ball-milled sample shows a low thermal conductivity of 1 W m−1 K−1, which is almost a constant below 300 K. However, due to its small grain sizes, the electron mobility is significantly decreased, thus their thermoelectric performances are not as good as that of the hand-milled sample. Also, below 25 K, the resistivity and the Seebeck coefficient of the ball-milled sample are decreased, which is associated with the energy barrier at their grain boundaries. Due to the larger grain sizes and fewer defects in the hand-milled sample, the external magnetic field shows a significant influence on its thermoelectric properties at low temperatures. These results indicate that polycrystalline ZrTe 5 with large grain sizes may exhibit similar quantum properties as those of single crystals. Image 1 • ZrTe 5 nanocomposites were synthesized by hand-milling and ball-milling. • Relation between the microstructure and thermoelectric properties is established. • Ball-milled sample has a very low thermal conductivity of 1 W m−1 K−1. • Magnetoresistance ratio is larger when grain size is bigger. [ABSTRACT FROM AUTHOR]

Cu–Cr–Zr alloys are often subjected to premature failures due to arc erosion at moment of their breakdown. In this paper, a series of simulated high-voltage arc ablation experiments were conducted to systematically investigate arc ablation characteristics of Cu–Cr–Zr alloys, their microstructure evolutions and anti-ablation properties after plastic deformation and microalloying. Results showed that during their arc ablation processes, a halo pattern was firstly formed on the surface under the action of high-temperature arc. This is followed by partial melting and splashing of Cu, forming of uneven and rough surfaces, and finally significant burning of the alloy. The degree of ablation of alloy is aggravated with the increased breakdown voltage. Due to a combined effect of solid solution strengthening, fine grain strengthening and deformation strengthening, the ablation resistance of the micro-alloyed and plastically deformed alloy has been significantly improved. The breakdown field strengths of commercial Cu–Cr–Zr alloy, heat-treated and deformed one, micro-alloyed and heat-treated one are 1.46 × 106 V/m, 1.67 × 106 V/m and 1.90 × 106 V/m, respectively. However, the breakdown strength of alloys after microalloying is unstable. Results show that there are no preferred phases for the first breakdown of arc ablation of Cu–Cr–Zr alloys. The second-phase particles with high-hardness and high-melting temperature hinder the splashing and flow of the molten copper, and inhibit the movement of the cathode spots during the ablation process. • Study the anti-arc ablation properties of plastic deformed and alloyed Cu–Cr–Zr. • The first breakdown of Cu–Cr–Zr is non-selective and forms halo in the surface. • The cathode spots expand to the surrounding area by the form of jumping. • The alloys after heat treated and deformed have excellent arc erosion resistance. [ABSTRACT FROM AUTHOR]