New ductile laminate structure of Ti-alloy/Ti-based metallic glass composite with high specific strength

Bulk laminate structure of Ti-alloy/Ti-based metallic glass composite(MGC) was prepared by melting a preform of alternate stack-up foils in the high vacuum atmosphere. The composite demonstrates a good combination of yield strength(~1618 MPa), plasticity(~4.3%) and specific fracture strength(384 × 10~3 Nmkg~(-1)) in compression. The maintained yield strength results from the unique microstructure composed of the Ti layer, the solution layer with gradient structure and the MGC layer. Such a multilayer structure effectively inhibits the propagation of shear band, leading to the enhanced plasticity. Those extraordinary properities suggest that combining ductile lamella with brittle metallic glass(MG) by such a lay-up method can be an effective way to improve mechanical properties of MG.     

Entropy generation in a heat exchanger working with a biological nanofluid considering heterogeneous particle distribution

Entropy generation rates considering particle migration are evaluated for a biologically produced nanofluid flow in a mini double-pipe heat exchanger. The nanofluid is used in tube side and hot water flows in annulus side. Silver nanoparticles synthesized through plant extract method from green tea leaves are utilized. Particle migration causes non-uniform concentration distribution, and non-uniformity intensifies by increase in Reynolds number and concentration. The results indicate that at high concentrations and Reynolds numbers, particle migration can have a great effect on entropy generation rates. For water inlet temperature of 308 K, the contribution of friction in nanofluid entropy generation is much more than that of heat transfer. However, as the water inlet temperature increases to 360 K, the heat transfer contribution increases such that at low Reynolds numbers, the thermal contribution exceeds the frictional one. For total heat exchanger, Bejan number is smaller than 0.2 at water inlet temperature of 308 K, while Bejan number has a large value at water inlet temperature of 360 K. Furthermore, entropy generation at the wall has an insignificant contribution, such that for Re = 1000 and φ_m = 1%, the total entropy generation rates for the nanofluid, wall, and water are 0.098810, 0.000133, and 0.041851 W/K, respectively.     

A first-principles investigation on mechanical and metallic properties of titanium carbides under pressure

The titanium carbides are potential candidates to achieve both high hardness and refractory property. We carried out a structural search for titanium carbides at three pressures of 0 GPa, 30 GPa and 50 GPa. A phase diagram of the Ti-C system at 0 K was obtained by elucidating formation enthalpies as a function of compositions, and their mechanical and metallic properties of titanium carbides were investigated systematically. We also discussed the relation of titanium concentration to the both mechanical and metallic properties of titanium carbides. It has been found that the average valence electron density and tractility improved at higher concentrations of titanium, while the degree of covalent bonding directionality decreased. To this effect, the hardness of titanium carbide decreases as the content of titanium increases. Our results indicated that the titanium content significantly affected the metallic properties of the Ti-C system.     

Al基块体金属玻璃的研究进展

Al基金属玻璃具有高强度、高韧性、良好的耐蚀性,特别是其比强度高达330kN·m/kg,作为新结构材料在航空航天领域具有潜在的应用前景。近年不仅研发出了具有大过冷液相区以及能形成块体金属玻璃的Al基合金,还通过粉体温热固化成形工艺实现了Al基金属玻璃的大块体化,推动了其在实际生产中的应用。简述了有关Al基金属玻璃合金的玻璃形成能力、过冷液体热稳定性、力学性能及其粉末烧结体的组织和性能等方面的最新研究进展,并对其发展存在的问题进行了探讨。     

Achieving superior mechanical properties in friction lap joints of copper to carbon-fiber-reinforced plastic by tool offsetting

It is a challenge to achieve a sound welded metal/carbon-fiber-reinforced thermoplastic (CFRTP) joint with high strength and few bubbles. In this study, sound lap joints of Cu and CFRTP were obtained by friction lap joining (FLJ) directly at rotation rates of 600–2000 rpm, with the welding tool at the joint center and offsetting the tool 7 mm away from the center toward the retreating side, respectively. Tool offsetting reduced the non-uniform temperature distribution in the lap joints resulting from the high conductivity of Cu, which not only enhanced the tensile shear force from 0.89–2.25 kN to 1.71–3.54 kN, with the maximum increasing rate of 135%, but also reduced the bubble area to only 19% of the original level of 2000 rpm. It is the first time to report a high-quality Cu/CFRTP joint with a high strength and few bubbles. The large increase of the strength after tool offsetting was attributed to the increase of the joining area, the decrease of bubbles and the decrease of the CFRTP degradation. The details on the generation, quantitative distribution and expulsion of the bubbles in the FLJ joints were discussed.     

Adsorption kinetics of malachite green onto activated carbon prepared from Tunçbilek lignite

Adsorbent (T₃K618) has been prepared from Tunçbilek lignite by chemical activation with KOH. Pore properties of the activated carbon such as BET surface area, pore volume, pore size distribution, and pore diameter were characterized by t-plot based on N₂ adsorption isotherm. The N₂ adsorption isotherm of malachite green on T₃K618 is type I. The BET surface area of the adsorbent which was primarily contributed by micropores was determined 1000 m²/g. T₃K618 was used to adsorb malachite green (MG) from an aqueous solution in a batch reactor. The effects of initial dye concentration, agitation time, initial pH and adsorption temperature have been studied. It was also found that the adsorption isotherm followed both Freundlich and Dubinin–Radushkevich models. However, the Freundlich gave a better fit to all adsorption isotherms than the Dubinin–Radushkevich. The kinetics of adsorption of MG has been tested using pseudo-first-order, pseudo-second-order and intraparticle diffusion models. Results show that the adsorption of MG from aqueous solution onto micropores T₃K618 proceeds according to the pseudo-second-order model. The intraparticle diffusion of MG molecules within the carbon particles was identified to be the rate-limiting step. The adsorption of the MG was endothermic (ΔH° = 6.55–62.37 kJ/mol) and was accompanied by an increase in entropy (ΔS° = 74–223 J/mol K) and a decrease in mean value of Gibbs energy (ΔG° = −6.48 to −10.32 kJ/mol) in the temperature range of 20–50 °C.     

Micro‐and Nanoscale Metallic Glassy Fibers

When bulk materials are made into micro‐and nanoscale fibers, there will be attractive improvement of structural and functional properties, even unusual experimental phenomena [Ref. 3 ]. The main drawback of various applications of metallic fibers is poor ability of present fabrication methods for controlling their dimensions and surface properties [Ref. 4 ]. Metallic glassy fibers (MGFs) are desired because of unique mechanical and physical properties and glass‐like thermoplastic processability of metallic glasses (MGs). Here, we report a synthetic route for production of micro‐to nanoscale MGFs (the diameter ranges from 100 µm to 70 nm) by driving bulk metallic glass rods in their supercooled liquid region via superplastic deformation. Compared with existing metallic fibers, the MGFs have precisely designed and controlled properties and size, high structural uniformity and surface smoothness, and extremely flexibility. Remarkably, the method is simple, efficient, and low cost, and the MGFs can be continuous prepared by the method. Furthermore, the MGFs circumvent brittleness of MGs by size reduction. We proposed a parameter based on the thermal and rheological properties of MG‐forming alloys to control the preparation and size of the fibers. The MGFs with superior properties might attract intensive scientific interest and open wide engineering and functional applications of glassy alloys.     

Direct joining of oxygen-free copper and carbon-fiber-reinforced plastic by friction lap joining

Oxygen-free copper(Cu) was successfully joined to carbon-fiber-reinforced thermoplastic(CFRTP,polyamide 6 with 20 wt% carbon fiber addition) by friction lap joining(FLJ) at joining speeds of 200–1600 mm/min with a constant rotation rate of 1500 rpm and a nominal plunge depth of 0.9 mm.It is the first time to report the joining of CFRTP to Cu by FLJ. As the joining speed increased, the tensile shear force(TSF) of joints increased first, and decreased thereafter. The maximum TSF could reach 2.3 kN(15 mm in width). Hydrogen bonding formed between the amide group of CFRTP and the thin Cu_2O layer on the Cu surface, which mainly contributed to the joint bonding. The influence factors of the TSF of the joints at different joining speeds were discussed. The TSF was mainly affected by the joining area, the degradation of the plastic matrix and the number and the size of bubbles. As the joining speed increased,the influence factors varied as follows: the joining area increased first and then decreased; the degradation of the plastic matrix and the number and the size of bubbles decreased. The maximum TSF was the comprehensive result of the relatively large joining area, small degradation of the plastic matrix and small number and sizes of bubbles.     

Solvothermal synthesis of Ag/ZnO micro/nanostructures with different precursors for advanced photocatalytic applications

Micro/nanostructured systems based on metallic oxide (ZnO) with noble metal (Ag) on the surface (Ag/ZnO) are synthesized by solvothermal method from zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O), zinc acetate dehydrate (Zn(CH₃COO)₂·2H₂O), zinc acetylacetonate hydrate (Zn(C₅H₇O₂)₂·xH₂O) and silver nitrate (Ag(NO₃)) as precursors. In these systems, polyvinylpyrrolidone (PVP) is used as surfactant for controlling particle morphology, size and dispersion. The obtained materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), UV–vis diffuse reflectance spectroscopy (DRS), N₂ gas adsorption–desorption (BET) and Raman spectroscopy (RS). By XRD results, all major peaks are indexed to the hexagonal wurtzite-type structure of the ZnO and samples with noble metal, extra diffraction peaks are detected which correspond to the face-centered-cubic (fcc) structure of the metallic Ag. Depending on used precursor, different morphologies have been obtained. Mainly, ZnO prims-like rods – NRs (with 0.8 ? aspect ratio ? 3.4) – have been observed. Quasi-spherical particles of metallic Ag (with diameters between 558 ± 111 μm and 22 ± 1 nm) have been detected on the ZnO surface. Photocatalytic results (all samples studied >30% MB degradation) verify the important effect of surfactant and the viability of synthesized Ag/ZnO micro/nanocomposites for environmental applications.     

Dynamic analysis of the scale-up of fluidized beds

A method is developed for hydrodynamics scale-up of gas-solid fluidized beds based on recurrence quantification analysis of nonlinear time series of pressure fluctuations. This method is an improvement of the previous method by including the entropy of pressure fluctuations to the list of scale-up parameters. Experiments were carried out at varying conditions, e. g., bed diameter (5, 9, 15, 40 and 80 cm ID), particle size (150, 300, 400 and 600 μm), bed height at aspect ratios (1, 1.5 and 2) and superficial gas velocities (ranging 0.1 to 1.7 m/s) to identify the main parameters that influence the dynamics and to develop a general interpretation of the analysis results. By investigation of the effect of operating parameters on entropy, a quantitative empirical correlation is proposed for including the entropy in the scale-up parameters. It was shown that this correlation improves the Glicksman’s method for the scale-up of fluidized beds.     

Microstructure correlated electrical conductivity of Manganese alloyed nanocrystalline cubic zirconia synthesized by mechanical alloying

Fully stabilized cubic (c) ZrO₂ phase has been synthesized by mechanical alloying (MA) the stoichiometric powder mixture of elemental Mn (5–20 mol%) and monoclinic (m) ZrO₂ at room temperature. XPS study reveals that major part of metallic Mn is ionized to Mn²⁺ oxidation state during MA. Mn-alloyed c-ZrO₂ nanoparticles with ～18 nm particle size have been synthesized within 10 h of MA. Microstructures of the compounds have been precisely evaluated by analyzing the X-ray powder diffraction patterns employing Rietveld refinement and transmission electron microscopy images. A decrease in lattice parameter from 5.11 Å to 5.09 Å is correlated with an increase in oxygen vacancy from 14% to 26% with increasing Mn concentrations. Elemental compositions in the compounds are obtained from electron probe microanalysis. The role of Mn alloying in the polymorphic phase transformation (m → c) has been established with changes in structure and microstructure parameters. Electrical conductivities of all c-ZrO₂ compounds are measured in the temperature range 350–550 °C. Grain and grain boundary contributions to total conductivity are calculated from frequency dependent real and imaginary impedance. Conductivity of Mn alloyed c-ZrO₂ increases with increasing temperature and Mn concentrations. Electrical transport mechanism in the compound is studied by impedance and modulus spectroscopy. The relaxation frequency is found to be temperature, microstructure and composition dependent.     

Amorphization and nanocrystalline Nb3Al intermetallic formation during mechanical alloying and subsequent annealing

In this paper the formation as well as the stability of Nb₃Al intermetallic compounds from pure Nb and Al metallic powders through mechanical alloying (MA) and subsequent annealing were studied. According to this method, the mixture of powders with the proportion of Nb-25 at% Al were milled under an argon gas atmosphere in a high-energy planetary ball mill, at 7, 14, 27 and 41 h, to fabricate disordered nanocrystalline Nb₃Al. The solid solution phase transitions of MA powders before and after annealing were characterized using X-ray diffractometry (XRD). The microstructural analysis was performed using scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM). The results show that in the early stages of milling, Nb(Al) solid solution was formed with a nanocrystalline structure that is transformed into the amorphous structure by further milling times. Amorphization would appear if the milling time was as long as 27 h. Partially ordered Nb₃Al intermetallic could be synthesized by annealing treatment at 850 °C for 7 h at lower milling times. The size of the crystallites after subsequent annealing was kept around 45 nm.     

Diaphragm forming of continuous fibre reinforced thermoplastics: influence of temperature,pressure and forming velocity on the forming of Upilex-R® diaphragms

In the diaphragm forming process, the thermoplastic composite sheet is clamped between two high temperature thermoplastic diaphragms. In the present study, the influence of temperature, pressure and forming rate on the deformation of high temperature PI diaphragms (Upilex-R^®, Ube Industries) is described. At temperatures below 275 °C the upper diaphragm slides over the bottom diaphragm and shows a more global deformation, above 305 °C, the upper diaphragm cannot slide over the bottom diaphragm and deforms in the same manner. The region 275–305 °C is a kind of transition region between the previous two temperature ranges. A hydrostatic pressure of 1 bar turned out to be sufficient to deform the diaphragms, therefore, no influence of pressure was observed. The deformation of the bottom diaphragm is independent of forming rate, while the upper diaphragm showed some dependence.     

A novel water permeable geopolymer with high strength and high permeability coefficient derived from fly ash,slag and metakaolin

In this work, a new water permeable geopolymer with high strength and high water permeability coefficient based on fly ash-slag-metakaolin was proposed. The experimental results show that fresh geopolymer composite exhibits dry characteristic and porous structure. The void ratio is 27.6% and the permeability coefficient reaches 1.70 cm/s. The compressive strength and flexural strength reach about 30 MPa and 6.2 MPa, respectively at 1 day and reach as high as 49 MPa and 11.3 MPa at 28 days of curing, respectively. After 100 freeze-thaw cycles, the terminal remaining mass is still larger than 80% along with internal damages and deteriorations on geopolymer paste coating. The dense microstructure of geopolymer matrix and interfacial transition zone indicates the high compressive strength, flexural strength and high freeze-thaw resistance of water permeable geopolymer.     

Effect of microwave irradiation on crystal growth of zeolitized coal fly ash with different solid/liquid ratios

In the present work, coal fly ash (CFA) was converted to zeolite (CFAZP) experimentally at atmospheric pressure via a conventional hydrothermal heating for 6 h at low temperature (90 ± 3 °C) followed by microwave irradiation for 30 min. The synthesized products were characterized using XRD, TGA/DTA, SEM, PSD, BET, and cation-exchange capacity (CEC) techniques. The effect of microwave on the crystal growth of nucleated CFAZP at different solid/liquid ratios (suspended CFA mass to NaOH solution volume, g/mL) was studied. A three-variable, three level central composite statistical experimental design was applied to investigate the effect of the independent variables on the response function defined as the ratio of the characteristic peak intensity at 2θ: 28° of a sample to that of the same peak of a sample run for 24 h with conventional heating. The relative peak intensity of CFAZP as high as 97% was achieved under optimum experimental conditions with 1 M of NaOH concentration, 6 h of conventional heating followed by 30 min microwave irradiation with a solid/liquid ratio of 0.40 g/mL. Under constant microwave energy, higher solid/liquid ratios led to higher relative peak intensity of the product.     

Development of high mechanical properties and moderate thermal conductivity cast Mg alloy with multiple RE via heat treatment

A new cast Mg–2 Gd–2 Nd–2 Y–1 Ho–1 Er–0.5 Zn–0.4 Zr(wt%) alloy was prepared by direct-chill semicontinuous casting technology. The microstructure, mechanical properties and thermal conductivity of the alloy in as-cast, solid-solution treated and especially peak-aged conditions were investigated. The as-cast alloy mainly consists of β-Mg matrix,(Mg, Zn)_3 RE phase and basal plane stacking faults. After proper solid-solution treatment, the microstructure becomes almost Mg-based single phase solid solution except just very few RE-riched particles. The as-cast and solid-solution treated alloys exhibit moderate tensile properties and thermal conductivity. It is noteworthy that the Mg alloy with 8 wt% multiple RE exhibits remarkable age-hardening response( HV = 35.7), which demonstrates that the multiple RE(RE = Gd, Nd, Y, Ho, Er) alloying instead of single Gd can effectively improve the age-hardening response.The peak-aged alloy has a relatively good combination of high strength/hardness(UTS(ultimate tensile strength) 300 MPa; TYS(tensile yield strength) 210 MPa; 115.3 HV), proper ductility(ε≈ 6%) and moderate thermal conductivity(52.5 W/(m K)). The relative mechanisms mainly involving aging precipitation of β￠ and β' phases were discussed. The results provide a basis for development of high performance cast Mg alloys.     

Co2(OH)3Cl nanoparticles as new-type electrode material with high electrochemical performance for application in supercapacitor

In this work, we report the preparation of Co₂(OH)₃Cl nanoparticles with average size of ～20 nm and well-defined cubic shape at room temperature by an epoxide precipitation route. It was found that the as-prepared Co₂(OH)₃Cl nanoparticles could be used as a promising new electrode material for application in redox supercapacitors due to its high electrochemical performance. It presented superior specific capacitance of 783 F g^?1 at low current density of 2.8 A g^?1, while it had a high value of 604 F g^?1 at high current density of 56.6 A g^?1, proving its excellent high rate performance. Its 75% capacitance retention after 10,000 cycles of charge–discharge demonstrated its long-life span. According to characterization results, the possible mechanism for the electrochemical process that Co₂(OH)₃Cl nanoparticles underwent was proposed as a process of Co₂(OH)₃Cl → β-Co(OH)₂ → CoOOH ? Co₃O₄.     

Characterization and properties of CuZrAlTiNi high entropy alloy coating obtained by mechanical alloying and vacuum hot pressing sintering

CuZrAlTiNi High entropy alloy (HEA) coating was synthesized on T10 substrate using mechanical alloying (MA) and vacuum hot pressing sintering (VHPS) technique. The MA results show that the final product of as-milled powders is amorphous phase. The obtained coating sintered at 950 °C is compact and about 0.9 mm in thickness. It is composed of a couple of face-centered cubic (FCC), one body-centered cubic (BCC) solid solutions and AlNi₂Zr phase. The interface strength between coating and substrate is 355.5 MPa measured by three point bending test. Compared with T10 substrate, the corrosion resistance of CuZrAlTiNi HEA coating is enhanced greatly in the seawater solution, which is indicated by the higher corrosion potential, wider passivation region, and secondary passivation. The average microhardness of the coating reaches 943 HV_0.2, and is about 3.5 times higher than the substrate, which is mainly ascribed to the uniformly dispersed nano-size precipitates, phase boundary strengthening and solid solution strengthening. Moreover, the wear resistance of the coating is slightly improved in comparison with the substrate.     

Atomic scale study of the dehydration/structural transformation in micro and nanostructured brucite (Mg(OH)2) particles: Influence of the hydrothermal synthesis conditions

Micro and nanostructured brucite (Mg(OH₂)) particles synthesized by hydrothermal method from solutions with high content of hydrazine (0.14 M) and nitrate (0.24 g) were compared with samples obtained from low hydrazine content (0.0002 M) and nitrate (0.12 g). The samples were heated at 180 °C for 4 h, 6 h and 12 h. XRD, TEM-HRTEM, SAED and image analysis techniques were used for the morphological and structural characterization. The effect of electron beam irradiation on the brucite dehydration was observed in atomic resolution images at 300 kV. Hexagonal crystals show differences in crystallinity, strains and kinetic of reaction. High hydrazine/nitrate samples have slightly larger crystals with better crystallinity, showing a strong preferential orientation. Rietveld refinements show how unit cell parameters are bigger in samples obtained with higher hydrazine/nitrate content, confirming also the preferential orientation along the 0 0 0 1 plane. Differences in the dehydration process show the rapid formation of a porous surface, the amorphised cortex or the presence of highly oriented strains in samples prepared from higher hydrazine/nitrate content. Conversely, crystals slightly smaller with randomly scattered defect surfaces showing the Mg(OH)₂/MgO interphase in samples prepared with low hydrazine/nitrate content. Significant differences in the kinetic of reaction indicate how the dehydration process is faster in samples prepared with high hydrazine/nitrate content.     

Dual structure O + B2 for enhancement of hardness in furnace-cooled Ti2AlNb-based alloys by powder metallurgy

Powder metallurgic Ti₂AlNb alloys were sintered at 900 °C, 990 °C, 1060 °C, and 1100 °C (i.e. in the O + B2, α₂ + B2 + O, α₂ + B2, and B2 phase region, respectively) for 12 h, followed by water quenching and furnace cooling. Quenching was employed to reserve the high-temperature phase and microstructure, and furnace cooling aimed to regulate the room-temperature microstructure for the enhancement of hardness. Widmanstatten B2 + O structure, which contributes to the properties, was induced from B2 crystals by sintering, unless the alloy was treated in the α₂ + B2 phase region. With the elevation of the sintering temperature, the content of α₂ phase became lower in the furnace-cooled alloys, and the hardness was improved accordingly. The highest hardness performance, 389 ± 23 HV, was obtained in the alloy solution treated in the single B2 region, and the alloy was comprised of complete O + B2 Widmanstatten structure.