Search

Heterostructure engineering is crucial for enhancing gas sensing performance. However, achieving rapid response for room-temperature NO2 sensing through rational heterostructure design remains a challenge. In this study, a Bi2Se3/SnSe22D/2D heterostructure was synthesized by hydrothermal method for the rapid detection of NO2 at room temperature. By combining Bi2Se3 nanosheets with SnSe2 nanosheets, the Bi2Se3/SnSe2 sensor demonstrated and the lowest detection limit for NO2 a short response time (15 s) to 10 ppm NO2 at room temperature, reaches 25 ppb. Furthermore the sensor demonstrates significantly larger response to NO2 than to other interfering gases, including 10 ppm NO2, H2S, NH3, CH4, CO, and SO2,demonstrating its outstanding selectivity. And we discuss the mechanism of related performance enhancement. [ABSTRACT FROM AUTHOR]

Ti-6554 (Ti-6Cr-5Mo-5V-4Al) alloy has attractive potential as a new structural material in the aviation field due to its excellent mechanical properties. However, it is expensive to manufacture, which can limit its application. Powder metallurgy (PM) is an economic technology to reduce the cost of titanium alloys. In this study, PM Ti-6554 alloy was prepared using irregular powder via vacuum sintering followed by forging. The influence of cooling rate (air cooling and water quenching) of as-forged sample on its microstructure was studied by scanning electron microscopy, electron backscatter diffraction and other analytical means. Experimental results showed that different cooling rates determined the structures of α and β phases. Compared with air-cooled sample, the water-quenched sample only had β phase microstructure without α phase precipitates. As-forged PM Ti-6554 alloy subjected to water quenching achieved ultimate tensile strength of 942 MPa and elongation of 20% and also had fine β grains of 10 μm. After solution treatment and aging, the sample exhibited high ultimate tensile strength (1211 MPa) and elongation (13.8%). Overall, PM Ti-6554 alloy possessed a good combination of high strength and reasonable ductility. This work marks a vital step forward in the application of high-performance PM Ti-6554 alloys. [ABSTRACT FROM AUTHOR]

Lithium-rich material (SOP) with special nano-micron composite structure is synthesized by simple one-step oxalic acid method. The SOP sample is made of micron particles (1–3 μm) and nano-particles (~ 100 nm). Compared with the co-precipitation prepared lithium-rich materials (COP), SOP has good rate performance and cycle stability. The specific discharge capacity of SOP sample reaches 104.2 mAh/g at 10 C, while that of COP sample is only 68.5 mAh/g. After 300 cycles, SOP still has a specific discharge capacity of 201 mAh/g and the capacity retention rate is 89.6%, while COP only has a specific discharge capacity of 135.8 mAh/g and the capacity retention rate is 58%. Structure allocation with nano-micron particles is conducive to electrochemical performance improvement. This study provides a new idea for the synthesis of lithium-rich material with better performance. [ABSTRACT FROM AUTHOR]

Powder metallurgy (PM) offers cost-effective potential for manufacturing titanium and titanium alloys. High oxygen content on titanium powder surface is a key problem affecting the mechanical properties of PM Ti alloys. Therefore, this study proposes a chloro-deoxidation method to reduce the oxygen content of titanium powder via introducing stannous chloride (SnCl2) into titanium powder. In the sintering process, SnCl2 reacts with the surface oxide on titanium powder to remove the oxide film, and thus forms gas TiClxOy escaping from Ti matrix, resulting in the decrease of oxygen content. With ~ 2.5 wt.% SnCl2 addition, the oxygen content reduces from 0.6 wt.% to 0.5 wt.%. Accordingly, the elongation of as-sintered Ti-SnCl2 sample significantly increases from 4.8% to 11% (increasing by 129%), while the tensile strength decreases from 815 MPa to 788 MPa. After HIP treatment, the elongation increases from 11% to 13%, and the strength is about 765 MPa. Although same Sn content (5 wt.%) is added in Ti samples, Ti-SnCl2 sample shows higher elongation value of 9.4% compared to Ti-Sn sample (3.6%), due to lower oxygen content. [ABSTRACT FROM AUTHOR]

The effects of solution-aging treatment on microstructure and mechanical properties of powder metallurgy (PM) Ti-6554 titanium alloy were investigated. PM Ti-6554 titanium alloy can achieve a good balance between strength and ductility after solution treatment at 810°C/30 min with furnace cooling and aging treatment at 520°C/6 h. Accordingly, the ultimate tensile strength, yield strength and elongation were 1360 MPa, 1323 MPa and 9.0%, respectively. The alloy had smaller α phase grain size (~ 0.69 μm), and its volume fraction was 73%. When the solution temperature increased from 810°C to 850°C, the ultimate tensile strength increased to 1601 MPa, the yield strength increased to 1543 MPa, and the elongation reduced to 3.5%. Microstructure results showed that the grain size of α phase gradually increased, while the volume fraction of α phase showed the opposite trend. When the solution temperature remained constant, slower cooling rate was beneficial to increase the alloy strength and maintain the strength-plasticity matching. [ABSTRACT FROM AUTHOR]

High oxygen Ti6Al4V alloys are fabricated by vacuum sintering and hot rolling using hydrogenation-dehydrogenation Ti6Al4V powder and ZrO2 powder as raw materials. The complete dissolution of oxygen and zirconium atoms results in an increase in lattice constant and strength. As-rolled Ti64-ZrO2 sample exhibits a bimodal structure with a fine acicular α phase of around 1 μm. Ti64-0.75 ZrO2 alloy with equivalent oxygen content close to 0.6 wt.-% presents a good combination of the high tensile strength (1180.2 MPa) and sufficient elongation (7.3%). Therefore, the critical oxygen content for the ductile-to-brittle transition of powder metallurgy Ti6Al4V alloy can be improved by suitable preparation methods. The formation of a fine β transformation structure may be one of the reasons for maintaining sufficient ductility. [ABSTRACT FROM AUTHOR]

In this study, phosphorus-containing Fe-5 wt.% Si silicon steel sheet was prepared by powder loose sintering followed by hot rolling. Defect-free sheet with high P content was achieved. The study found that P effects on sintering promotion and processing deterioration were significantly suppressed by the presence of Si in steel. Appropriate P content would significantly improve the mechanical and magnetic properties of the sample. Under a comprehensive consideration, P content of 0.3-0.5 wt.% was suitable for silicon steel. Compared with P-free silicon steel, with 0.3 wt.% P addition, the tensile strength of silicon steel increased from 521 MPa to 680 MPa. As to the magnetic performance, the sample with 0.5 wt.% P had B8 of 1370.5 mT, and W10/50 0f 1.16 W·kg−1, while those for P-free sample were 1332.3 mT, and 1.46 W·kg−1, respectively. FeP phase with special morphology would be precipitated in samples with P addition. [ABSTRACT FROM AUTHOR]

This study provides an effective surface modification method for Li-rich layered oxide (LLO, Li1.2Mn0.54Ni0.13Co0.13O2) with Al2O3 coating. Strong organic acid TFBDC (2,3,5,6-tetrafluoro-1,4-phthalic acid) accumulates near alkali metal oxide LLO to form uniform Al-TFBDC coating. Al-TFBDC modified LLO is subjected to heat treatment to form Al2O3 coating on the surface of LLO. This uniform coating protects LLO from direct contact with electrolyte and does not block the migration of Li+. Meanwhile, F− is successfully doped into LLO particles. The LLO coated with doping has clear layer structures, and its electrochemical properties have been significantly improved. The rate performance is increased by 66% at 10 C. After 150 cycles, its capacity retention rate is 92.5%, while that of uncoated LLO is only 55.8%. [ABSTRACT FROM AUTHOR]

Although 3D printing of titanium alloys is often obtained by laser fusion deposition, its cost is relatively high. In this study, one light‐curing‐assisted technique is designed to print porous Ti6Al4V alloys via direct ink writing (DIW). For printing, titanium alloy slurry with 45 vol% solid content is prepared based on 1,6‐hexanediol diacrylate monomer‐trimethylolpropane triacrylate monomer (HDDA‐TMPTA) photosensitive system. In such a case, the extruded filament was in situ cured under the action of UV light irradiation in the printing process. The printed lattice sample has good surface performance without the observation of a collapse. After sintering, the shrinkage percentage is around 16% in the horizontal direction and 19% in the vertical direction. Surface morphology does not change significantly. Through comparative tests, it is found that the sintered samples have good microstructure and mechanical properties. When the filling rate is 50%, the compressive strength could reach 604.7 MPa and the flexural strength is 106.8 MPa. The feasibility of this new printing method to prepare titanium alloy parts are confirmed. [ABSTRACT FROM AUTHOR]

Powder metallurgy high-silicon steel strip (Fe–6.5 wt-% Si) was prepared by directly sintering followed by rolling using gas atomised powder with low oxygen content. Due to its poor formability, the gas atomised powder was directly sintered with something heavy of 1 kg overlaid on powder top. The relative density of sintered samples was about 94.1% and the porosity was 5.9%. The pore pinning effect prevented the formation of extremely large grains during sintering, which was beneficial for subsequent rolling. The grain size was controlled in the range of 100–300 μm. After cold rolling, a large number of sub-grain boundaries and deformation bands were generated, which increased the strength to 1190 MPa. It was worth noting that these two would disappear after annealing. Instead, ordered B2 and D03 phases were formed, and the texture of high-silicon steel was mainly {100}<110>. A low iron loss W10/50 value of 0.55 W kg−1 was achieved. [ABSTRACT FROM AUTHOR]

In this work, copper ferroalloys (CFAs) with various Fe contents (5, 10 and 30 wt-%) were fabricated via the mechanical alloying and vacuum sintering method, followed by hot and cold rolling. Microstructure, mechanical, electrical and magnetic properties were investigated using scanning electron microscopy (SEM), X-Ray diffraction (XRD), tensile testing, four-point probe, vibration sample magnetometer and dc BH circuit tracer, respectively. The CFAs with homogenous and fine in-situ Fe particles prepared by powder metallurgy showed better performance compared with previously reported conventional casting. After annealing at 400°C, the cold-rolled CFA with 30 wt-% Fe had the tensile strength of 621 MPa, the electrical conductivity of 50.2% IACS, magnetic saturation strength (Ms) of 60.39 emu g−1 and coercivity (Hc) of 98.2 Oe, achieving a good combination of mechanical and functional properties. Relations between the microstructure and mechanical and functional properties are discussed in detail. [ABSTRACT FROM AUTHOR]

Powder metallurgy (PM) Ti6Al4V alloy was prepared from HDH alloy powder by vacuum pressureless sintering. To study its high-temperature deformation behaviour, isothermal compression testing was carried out with temperature range of 900–1050°C, strain rate range of 0.01–10 s−1, and compression ratio of 60%. Based on the hot deformation data, the corresponding constitutive equation and hot processing map were clarified. The deformation activation energy for PM Ti6Al4V alloy was 606.5 kJ mol−1. Its deformation instability zone was very small, locating in the range of 960∼990°C with strain rate >1 s−1. PM Ti6Al4V alloy had large hot working window and good hot workability. The ideal hot processing domain was at 970–990°C and 0.05–0.01 s−1. Besides, the domain at 1000–1040°C and 1–10 s−1 was also suitable for hot processing. This study proposed an effective guidance for the hot deformation (e.g. forging, extrusion, rolling) of PM Ti6Al4V alloy. [ABSTRACT FROM AUTHOR]

In this study, a novel W and TiO2 synergistic strengthened copper matrix nanocomposite was prepared by a powder metallurgy route with a mechano-chemical method and subsequent consolidation. Nano-sized W and TiO2 particles in the composite powder were fabricated by solid-phase reaction during the mechanical alloying procedure. The average sizes of W and TiO2 particles were only 51 and 171 nm, far finer than single-phase particle-strengthened composites. It was found that the nanoparticles effectively resisted the grain coarsening in the copper matrix, containing the grains with an average size of 350 nm. The ultimate tensile strength and electrical conductivity of the copper composite are 520 MPa and 74 IACS%, achieve an ideal trade-off between them. The observations suggested that the nanoparticles were highly uniformly dispersed in the copper matrix, and the particle coarsening was restrained as the results of the interaction effects between W and TiO2 nanoparticles. [ABSTRACT FROM AUTHOR]

In addition to wave‐based fields, metamaterials can manipulate diffusion fields at will, for example, the scattering cancellation of particle flow in natural materials. In this paper, a monolayer cloak is proposed to eliminate electron scattering and improve the total conductivity in commonly used aluminum‐oxide‐dispersion‐strengthened copper alloys (Cu‐Al2O3) after a multiscale model is established to theoretically explain the dependence of conductivity on scattering behavior. Intense electron scattering caused by dispersed alumina nanoinclusions dominates the drastic drop in the conductivity in the Cu‐Al2O3 system. The Drude model is expanded to a generalized form to explain the multiscale scattering regime in Cu‐Al2O3 after unifying the macro‐ and nanoscale considerations into the mesoscopic multibody scattering process of a Monte Carlo simulation. The results indicate that the conductivity is closely related to the overall electron density and relaxation time of electrons. Then, a cloak is designed based on scattering cancellation to improve the conductivity by reducing electron collisions, whose structure is simplified into a monolayer cloak by adopting an imaginary insulating layer. Both simulation and experiment confirm a substantial improvement of the total conductivity. The invisible cloaks manipulating particle flow expands the research scope of metamaterials to innovatively improve the properties of traditional materials. [ABSTRACT FROM AUTHOR]

Fe-3.3Si-6.5Cr powders were first treated by phosphoric acid solution and then mixed with epoxy-modified silicone resin uniformly, forming insulation coating. The Fe-3.3Si-6.5Cr soft magnetic composites were prepared by compaction and annealing treatment of the coated Fe-3.3Si-6.5Cr powders. The microstructure and composition of Fe-3.3Si-6.5Cr powders were analyzed by scanning electron microscope coupled with energy-dispersive spectrometer, Fourier-transform infrared spectra, and X-ray photoelectron spectroscopy, respectively. The magnetic properties were determined by the LCR bridge tester and an auto testing system for magnetic materials (MATS-2010SA). Results show that both proper phosphating treatment and annealing at higher temperature can improve the permeability and reduce the core loss of the Fe-3.3Si-6.5Cr SMCs. When the concentration of phosphoric acid was 0.5 wt% and the heat treatment temperature reached 500 °C, the Fe-3.3Si-6.5Cr SMCs showed the optimized magnetic properties, including the permeability (μe) of 44.7 H/cm, the core loss (P) of 521.8 mW/cm3 at the saturated magnetic flux density of 50 mT, and the frequency of 100 kHz. The Fe-3.3Si-6.5Cr SMCs with distinguished magnetic properties provide great application prospect in various fields such as filter inductors, transformers, and sensors. [ABSTRACT FROM AUTHOR]

In this paper, powder metallurgy (PM) H13 steels were investigated based on the characterisation of water atomised H13 powders. Vacuum sintering was carried out from 1150 to 1265°C for sintering densification. The relative density of the as-sintered sample reached to 95% and mechanical properties were released above 1200°C. To eliminate the residual pores, subsequent forging was performed. The relative density increased to above 99%. As the concentration of Si elements on the powder surface was higher than the nominal composition, there was Si segregation in the form of silicon oxides (1–3 μm). Although oxide particles such as SiO2 were inevitable, the mechanical performance of PM H13 steels was still comparable to that of ingot metallurgy products. The tempered PM H13 steels exhibited high tensile strength of 1460 MPa in YS, 1737 MPa in UTS and 8.7% in elongation. Besides, the impact toughness was as high as 14.7 J cm−2. [ABSTRACT FROM AUTHOR]

A novel and quick process combining self-propagating reaction with vacuum-expendable pattern casting is presented to accomplish integrated preparation of millimeter-thick TiCp/Al composite coatings on the Al substrate. Titanium and graphite powders were mixed with the polytetrafluoroethylene (PTFE) additive and pasted on the expendable polystyrene (EPS) followed by compaction. Al components with in situ TiCp/Al composite coating were simultaneously synthesized at a relatively low temperature of molten Al, which was poured into the assembly of EPS and powder compact inside the silica sands. Differential scanning calorimetry, x-ray diffraction, scanning electron microscopy with energy-dispersive spectroscopy and transmission electron microscopy were used to systematically investigate the thermodynamic characteristics of the reaction, the phase constituents, microstructure and tribological properties of the coatings. The infiltration model describing the densification of the reaction coatings was also developed for the critical wetting condition. The wear characteristics were assessed using a pin-on-disk tribometer with various loads. Results showed that uniform TiC particles stimulated by the PTFE-activated self-propagating reaction afforded superior mechanical properties and wear resistance. [ABSTRACT FROM AUTHOR]

Damage mechanics based on the cohesive zone model were applied to study the anodic dissolution stress corrosion cracking (SCC) in flat and U-shaped edge-notched specimens. The simulation results show that corrosion product films (CPFs) facilitate crack initiation in SCC due to the CPF-induced stress and CPF rupture. In the flat specimen, SCC susceptibility increases with the CPF thickness and CPF Young's modulus, while it decreases with CPF fracture strength. For the U-shaped edge-notched specimen, the normalised threshold stress intensity factor KISCC/KIC decreases with the CPF thickness and notch depth. [ABSTRACT FROM AUTHOR]

With higher power, frequency and longer life of microwave tubes, cathode heater assembly is being modified to enhance the warm-up performance and reliability, which are governed by ceramics thermal conductivity, electrical resistivity and shrinkage. In present work, a potting material with a high thermal conductivity of 22.14 W/(m K) and low linear shrinkage of 5.5% was prepared using two kinds of alumina powders with different size and morphology. Aqueous slurries were produced for centrifugal casting. The highest solid loading slurries with 70 vol.% were obtained. Green body with relative density above 70% was easily made from slurries using centrifugal casting. Relative sintered density reached 86.75% maximum without any sintering aids. Rheological behavior of slurries, potting microstructure, sintering shrinkage and thermal conductivity were analyzed. Continuous particle distribution, series and parallel models were used to guide the powders proportion and explain the thermal conductivity. The potting material thermal conductivity experimental data agreed with the series and parallel models when the weight parameter ξ was between 0.3 and 0.5. [ABSTRACT FROM AUTHOR]

Microstructure evolution and variations in mechanical properties of Al-Al2O3 nanocomposite produced by powder metallurgy were investigated and compared with commercially pure aluminum (Al-1050) after furnace annealing. Fine gas-atomized Al powder compacts were first sintered in flowing nitrogen, subsequently consolidated into wires by rotary swaging and eventually annealed at 300 and 500 °C for 24 h each. Scanning and transmission electron microscopy with energy-dispersive spectroscopy was utilized to document the microstructure evolution. Rotary swaging was proven to lead to a marked decrease in grain size. After heavy swaging to true deformation degree of φ = 6 and annealing at 500 °C, obvious recrystallization was observed at Al-1050’s existing grain boundaries and the crystals began to grow perpendicular to the flow direction. In the Al-Al2O3 nanocomposite, fabricated from d50 = 6 μm Al powder, recrystallization partially occurred, while grains were still extremely fine. Due to the dual role of fine-grained Al2O3 dispersion strengthening, the nanocomposite showed improved mechanical performance in terms of tensile strength, approximately twice higher than Al-1050 after annealing at 500 °C. [ABSTRACT FROM AUTHOR]

In this work, Al-Zn-Mg-Cu powders containing 0.15 and 0.33 wt % oxygen were utilized to prepare high-strength aluminum alloys through the process of cold isostatic pressing, sintering, hot extrusion, and heat treatment. Microstructural and mechanical properties at elevated temperatures of 250, 350, and 450 °C were investigated by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and high-temperature tensile tests. Results showed that the tensile strengths of the obtained Al-Zn-Mg-Cu alloys with 0.15 wt % oxygen were 185, 46, and 18 MPa at 250, 350, and 450 °C, respectively. When the oxygen content of Al-Zn-Mg-Cu alloy rose to 0.33 wt %, the tensile strengths at the corresponding temperature reached up to 205, 68, and 25 MPa, respectively. The excellent high-temperature performance could be attributed to double hindrance to dislocation motion and grain boundary migration by a large amount of nano γ-Al2O3 created by the in-creased oxygen, thereby resulting in fine grains even at high temperatures. [ABSTRACT FROM AUTHOR]

Preparing high relative density γ-TiAl alloy by pressure-less sintering at low-cost has always been a challenge. Therefore, a new kind of non-spherical pre-alloyed TiAl powder was prepared by the reaction of TiH2 powder and Al powder at 800 °C to fabricate high-density Ti-48Al alloy via pressure-less sintering. The oxygen content was controlled to below 1800 ppm by using coarse Al powder (~120 μm). The sintered densities ranged from 92.1% to 97.5% with sintering temperature varying from 1300 °C to 1450 °C. The microstructure of the sintered compact was greatly influenced by the sintering temperature. The as-sintered samples had a near-γ structure at 1350 °C, a duplex structure at 1400 °C, and a nearly lamellar structure at 1450 °C. To achieve full densification, non-capsule hot isostatic pressing was performed on the 1350 °C and 1400 °C sintered samples. As a result, high compressive strengths of 2241 MPa and 1931MPa were obtained, which were higher than the existing Ti-48Al alloys. [ABSTRACT FROM AUTHOR]

Highly-aligned flake graphite (FG) reinforced Cu matrix composites with high thermal conductivity and adaptive coefficient of thermal expansion were successfully prepared via the collaborative process of tape-casting and hot-pressing sintering. To overcome the problem of fragile interface, Zr-Cu alloy powder was introduced instead of pure Zr powder to enhance the interfacial strength, ascribed to the physical-chemical bonding at the Cu-FG interface. The results indicate that the synthetic ZrC as interfacial phase affects the properties of FG/Cu composites. The thermal conductivity reaches the maximum value of 608.7 W/m∙K (52% higher than pure Cu) with 0.5 wt % Zr. Surprisingly, the negative coefficient of thermal expansion (CTE) in the Z direction is acquired from −7.61 × 10−6 to −1.1 × 10−6/K with 0 to 2 wt % Zr due to the physical mechanism of strain-engineering of the thermal expansion. Moreover, the CTE in X-Y plane with Zr addition is 8~10 × 10−6/K, meeting the requirements of semiconductor materials. Furthermore, the bending strength of the FG/Cu-2 wt % Zr composite is 42% higher than the FG/Cu composite. Combining excellent thermal conductivity with ultralow thermal expansion make the FG/Cu-Zr composites be a highly promising candidate in the electronic packaging field. [ABSTRACT FROM AUTHOR]