Influence of Deep Cryogenic Treatment on Microstructures and Mechanical Properties of an Ultrafine-Grained WC-12Co Cemented Carbide

Effect of deep cryogenic treatment(DCT) on the microstructures and mechanical behavior of ultrafine-grained WC-12 Co cemented carbide was investigated by using XRD, SEM, and DSC. The phase transformations of pure Co and binder phase Co in cemented carbide were analyzed in detail to correlate the strengthening mechanism with its a→ε phase transition. The results show that DCT resulted in a slight increase in hardness and bending strength of ultrafinegrained WC-12 Co cemented carbide. For the ultrafine-grained cemented carbide after DCT, there is no significant change in the microstructure and the elemental distribution of the cemented carbides, but the fractured morphology shows a feature of plastic deformation. In the cases of pure Co and the binder phase Co in WC-12 Co cemented carbide, they exhibit different features of phase transformation. The improvement of mechanical property of cemented carbide can be attributed to the increased amount of e-Co in WC-12 Co composites after DCT.     

Shape Memory Alloy-Reinforced Metal-Matrix Composites:A Review

Metal-matrix composites reinforced with shape memory alloys(SMA, including long fiber, short fiber, and particle) are ‘‘intelligent materials' ' with many special physical and mechanical properties, such as high damping property,high tensile strength, and fatigue resistance. In this review article, the fabrication method, microstructure, interface reaction, modeling, and physical and mechanical properties of the composites are addressed. Particular emphasis has been given to(a) fabrication and microstructure of aluminum matrix composites reinforced with SMAs, and(b) shape memory effect on the physical and mechanical properties of the composites. While the bulk of the information is related to aluminum matrix composites, important results are now available for other metal-matrix composites.     

Effect of Isothermal Temperature on Microstructure and Mechanical Properties of High AI-Low Si TRIP Steel

In this study, the effect of isothermal temperature on microstructure and mechanical properties of a high Al-low Si TRIP steel was investigated using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, electron back scattered diffraction, and tensile test. The results show that typical microstructure containing ferrite, bainite, and retained austenite can be obtained when two-stage heat treatment process was utilized. When annealing temperature is 840 ℃ and austempering temperature is 400 ℃, the tensile strength is 542 MPa and the product of strength and elongation is 17,685 MPa%. The morphologies and stability of the retained austenite in low silicon/high aluminum TRIP steel were finally discussed.     

Influence of Temperature on in Nanocrystalline Materials： the Inverse Hall-Petch Effect Phase Field Crystal Simulation

The influence of temperature on the inverse Hall-Petch effect in nanocrystalline(NC) materials is investigated using phase field crystal simulation method.Simulated results indicate that the inverse Hall-Petch effect in NC materials becomes weakened at low temperature.The results also show that the change in microscopic deformation mechanism with temperature variation is the main reason for the weakening of the inverse Hall-Petch effect.At elevated temperature,grain rotation and grain boundary(GB) migration seriously reduce the yield stress so that the NC materials exhibit the inverse Hall-Petch effect.However,at low temperature,both grain rotation and GB migration occur with great difficulty,instead,the dislocations nucleated from the cusp of serrated GBs become active.The lack of grain rotation and GB migration during deformation is mainly responsible for the weakening of the inverse Hall-Petch effect.Furthermore,it is found that since small grain size is favorable for GB migration,the degree of weakening decreases with decreasing average grain size at low temperature.     

Pulse-plating electrodeposition and annealing treatment of CulnSe2 films

CuInSe2 （CIS） thin film was prepared on molybdenum substrate using pulse-plating electrodeposition in aqueous solution. The most suitable pulse potential range for co-deposition is found to be from -0.55 to -0.75 V （vs SCE） from linear potential scanning curve. The electrodeposited films were characterized by X-ray diffractometry （XRD）, scanning electron microscopy（SEM） and energy dispersive X-ray analysis （EDS）. The annealing effects on electrodeposited precursors were investigated. And the influence of pulse parameters on film quality was studied. The chalcopyrite phase CulnSe2 films with smooth surface and stoichiometric composition are obtained at a pulse potential from -0.65 to -0.7 V （vs SCE）, a pulse period of 1-9 ms with a duty cycle of 33% and annealing treatment.     

Wettability of TiAl alloy melt on ceramic moulds in electromagnetic field

In the electromagnetic field, the wettability between Ti50Al alloy melt and oxide ceramic moulds was studied by the self-designed measuring apparatus. The thermodynamic and kinetic laws and mechanism on wetting were studied systematically. The results show that in the electromagnetic field, the order of contact angles for the molten Ti50AI alloy for the eight oxide materials is θ（Y203） 〉 θ（ZrO2（Y203）） θ〉 0（ZrO2（CaO）） θ〉 0（CaO） ：〉 θ（ZrO2（MgO）） θ〉 0（A1203） θ〉 0（Zircon） ：〉 θ（MgO）. The wetting process of Ti50Al alloy and ceramic moulds includes the nonreactive wetting at the first stage, and the reactive wetting at the final stage. And the higher the ceramic chemical stability, the longer the nonreactive wetting time.     

Microstructure and properties of 7A52 A1 alloy welded joint

7A52 A1 alloy plate aged at 105℃ for 8 h and then at 130℃ for 24 h was welded by means of TIG using A1- 6.3Mg-0.35Sc-0.1Zr-0.1Cr solder wire. Mechanical properties and microstructures of welded joint were studied. There are two obviously soft areas in the welded joint, welding seam and over-aging zone. The mechanical properties of welded joint are that σb is 358 MPa, σ0.2 is 238 MPa and δ5 is 6.6%. 75.6% of welding coefficient can be achieved. The addition of scandium leads to very significant grain refinement in the fusion zone, which results in a reduction in solidification cracking tendency. The solidification cracking isn＇t observed.     

Microstructure and Mechanical Ultra-High Strength Hot-Rolled Refuge Chamber Properties of 1,000 MPa Plate Steel for Coal Mine

The 1,000 MPa ultra-high strength hot-rolled plate steel with low-carbon bainitic microstructure was developed in the laboratory for coal mine refuge chamber. The static recrystallization behavior, microstructure evolution, and mechanical properties of this hot-rolled plate steel were investigated by the hot compression, continuous cooling trans- formation, and tensile deformation test. The results show that the developed steel has excellent mechanical properties at both room and elevated temperature, and its microstructure mainly consists of lath bainite, granular bainite, and ferrite after thermal-mechanical control process （TMCP）. The ultra-high strength plate steel is obtained by the TMCP process in hot rolling, strengthened by bainitic transformation, microstructure refinement, and precipitation of alloying elements such as Nb, Ti, Mo, and Cu. The experimental steel has relatively low welding crack sensitivity index and high atmospheric corrosion resistance index. Therefore, the developed steel has a good balance of strength and ductility both at room and elevated temperature, weldability and corrosion resistance, and it can suffice for the basic demands for materials in the manufacture of coal mine refuge chamber.     

Microstructure and Properties of In Situ Si and Fe-rich Particles Reinforced AI Matrix Composites Assisted with Ultrasonic Vibration

In this research, the in situ Si and Fe-rich particles reinforced Al matrix composites were fabricated by rheocasting （RC） process assisted with ultrasonic vibration （USV）. After USV treatment, the polygonal primary Si crystals were refined into particles with average diameter of about 15-23 μm, and the fraction of primary Si declined to about 5.4-6.5 vol%. The coarse plate-like δ-Al4（Fe,Mn）Si2 phase was transformed into fine particles with average diameter of about 17-20 μm, and the fraction of particle-like Fe-bearing particles is about 3.6-5.3 vol%. The ultimate tensile strength of the RC composites increases with the increase of Fe content at 350 ℃. The increase of the elevated temperature strength of the composites is mainly attributed to the refinement of δ-Al4（（Fe,Mn）Si2 phase and the increase of the volume fraction of the Fe-bearing compounds. Compared with the composites without USV, the RC composites assisted with USV have thinner mechanical mixing layer in wear test, which corresponds to smaller wear rate.     

Mechanism of fluidized chlorination reaction of Kenya natural rutile ore

In this paper, the thermodynamics and kinetics of nature rutile carbochlorination in a fluidized-bed were investigated. The thermodynamic calculations of TiO2–C–Cl2system show that when C is excess in the solid phase,titanium tetrachloride and carbon monoxide can exist stably. At high temperature, the reaction with CO as the product is the dominant reaction. The appropriate reaction conditions are as follows: reaction temperature of 950 °C,reaction time of 40 min, carbon ratio of 30 wt% of rutile,natural rutile particle size of-96 lm, petroleum coke size of-150 lm, and chlorine flow of 0.036 m3 h-1. Under the above conditions, the reaction conversion rate of TiO2 can reach about 95 %. This paper proposed a reaction rate model, and got a rutile chlorination rate formula, which is generally consistent with the experimental data. For the TiO2–C–Cl2system, the reaction rate is dependent on the initial radius of rutile particle, density, and the partial pressures of Cl2. From 900 to 1,000 °C, the apparent activation energy is 10.569 kJ mol-1, and the mass diffusion is found to be the main reaction-controlling step. The expression for the chlorine reaction rate in the C–Cl2system is obtained, and it depends on the degree of reaction,the partial pressure of Cl2, and the size of rutile particle.     

Finite Element Simulations of Crack Propagation in Al_2O_3/6061Al Composites

In this work, the local fracture initiation behaviour of an Al2O3/6061 Al composite is studied numerically. The damage behaviour of the microstructure is evaluated in consideration of the path and the amount of damage as well as the stress–strain performance of the microstructure. The damage behaviour of the ductile matrix has been simulated using the damage parameter D. For the simulation of fracture of the ceramic particles, a normal stress criterion is applied. For the analysis of the damage behaviour of the transition zone between particulate and matrix, both damage models(D parameter and normal stress criteria) are applied in this region. Parameter studies of crack propagation prediction in the Al2O3/6061 Al composite on the basis of an Element Elimination technique have been performed for two differently heat-treated variants resulting in different mechanical properties. In addition, residual stress effects on the damage behaviour are examined for various microstructural situations.     

Characteristic evaluation on spray-deposited WFTO thin films as a function of W doping ratio

In this work, F and F+W simultaneously doped SnO2 highly transparent conducting thin films were deposited on glass substrates at(500 ± 5) °C temperature by the spray pyrolysis method. Microstructural, morphological,electrical and optical properties of FTO films were investigated as a function of tungsten(W) doping, in the range from0 to 5 at%. X-ray diffraction patterns show that the films exhibit a tetragonal cassiterite structure and(200) preferential orientation of FTO film, and the relative strength of these peaks changes with altering the W doping ratio. The preferred growth of(211) changed to(200) plane with 2 at% W doping level and 3 at% W-doped film had(200) orientation and with further doping, this changed to(110) orientation.The scanning electron microscopy and atomic force microscopy images of the films indicate that the films are made up of dense small particles of a pyramidal shape and have a smooth surface. It was observed that the surface morphology of the films did not change much when the W element was inserted to the FTO structure. It was found that the sheet resistance values of the films varied with W doping ratio, and 2 at% W-doped FTO thin film exhibited the lowest values of sheet resistance(1.12 X). Also, the highest figure of merit, infrared reflectivity and optical band gap values were calculated for 2 at% W-doped FTO film as 50.9 9 10-2X-1,98.82 % and 4.13 eV, respectively. These results make the films an effective candidate for usage in many optoelectronic applications and photo-thermal conversion of solar energy.     

Route Effect on Equal Channel Angular Pressing of Copper Tube

A new technique to produce ultra-fine grained tubular specimen has been proposed,and the experiments have been performed using equal channel angular pressing(ECAP) with an angle of 90° between two intersecting channels and also the use of rubber pad as a mandrel during process.Commercial purity copper tubes have been pressed up to three passes through four different fundamental routes(A,B_A,B_C,and C) directions of which are identified in the text below.The influence of each route on the value,distribution,and homogeneity of hardness has been investigated by applying Vickers micro-hardness measurements at various locations of the tube's transverse planes.Significant enhancement of the hardness is observed after the first pass ECAP.Also,routes C and B_C show,respectively,better average hardness magnitude and hardness distribution uniformity.In addition,the results indicate that there is about 50%and 62%reduction of the grain size,compared to the annealed condition,following ECAP process of the copper tube sample after the first and the third pass via route B_C.     

Optimization and mechanism of gold-bearing sulfide flotation

In order to overcome the difficulty of extracting gold from gold-bearing sulfide ore by cyanide process flotation was adopted based on mineralogical analysis Mineralogy shows that gold particles are of superfine structure and mainly enclosed by sulfide ores. Primary gold-bearing sulfide ore is fine-grained pyrite and arsenopyrite. The paper describes the effects of ratios and dosage of activators and collectors on the recovery and grade of gold concentrate. A proper flotation flowsheet was then proposed based on experimental condition and closedcircuit test. The gold concentrate with the gold grade of25.14 g ton-1and the recovery of 86.94 % is obtained after one rougher, three cleaners, and four scavengers from fine grinding flotation process. Furthermore, the mechanisms of combined activators and combined collectors were studied by thermodynamic calculation, and structure–activity relationship of flotation reagent was also explained     

Influence of hydrogenation on microstructures and microhardness of Ti6A14V alloy

The microstructures of Ti6A14V alloy after hydrogenation were investigated by optical microscopy（OM）, X-ray diffraction（XRD） and transmission electron microscopy（TEM）. The influence of hydrogenation on the hardness of α and β phases was analysed by microhardness testing. The influence of hydrogenation on alloying elements diffusion was studied by electron probe microanalysis（EPMA）. The microstructural observation reveals that hydride δ （FCC structure） as well as large number of dislocations precipitate in the specimens with 0.278% and 0.514% hydrogen, and a lot of twins are found in the specimen with 0.514% hydrogen, simultaneously. The result of microhardness testing shows that the hardness of a and β phases increases synchronously with the increase of hydrogen and the hardness increment of β is larger than that of a. According to analysis of EPMA, the diffusion ability of alloy elements Al and V increases after hydrogenation. It is considered that hydrogen solution strengthening and V element diffusion are the main factors causing the hardness of a phase increase with the increase of hydrogen, and the formation of δ hydrides, lattice defects, hydrogen solution strengthening and Al element diffusion jointly cause the hardness of β phase increase with the increasing hydrogen.     

Micellar sensitized catalytic kinetic spectrophotometry for highly accurate and reproducible determination of V（IV） and V（V）

A highly accurate and reproducible micellar sensitized kinetic method was proposed for determination of V（VI）. The method is based on its catalytic effect on the oxidation of Coomassie brilliant blue R 250 （CBB＋） by bromate at pH 2.0. The reaction was monitored spectro- photometrically by measuring absorbance change with a fixed-time method of 5 min at 594 and 552 nm with and without surfactant. The variables influencing the calibra- tion sensitivity were extensively investigated, and the optimal conditions were established. The linear calibration range was 10-1,600 μg.L-1 with a relative SD ranging from 0.35 % to 3.35 % （for five replicate measurements of 75, 500, 1,000, and 1,500 μg.L-1） and a detection limit of 3.8 μg.L-1. The selectivity was also investigated, and greatly enhanced by suitable masking agents. The method was successfully applied to the analysis of V（IV） in pre- sence of excess V（V） up to 25 fold in environmental waters with the recoveries of 100.0 %-102.8 % for V（IV） and 95.7 %-99.7 % for total V. Its accuracy was validated by analysis of certified reference material via the present kinetic method and standard flame atomic absorption spectrometric method after extractive preconcentration with good agreement between certified and found values.     

Preparation and application in electromagnetic absorption of ZnO/FeNiMo composite

In order to increase the absorbing ability and expand the absorbing bandwidth, ZnO and FeNiMo particles were established as absorbers, and wax as adhesive, and the electromagnetic parameters were tested using a vector network analyzer, then the absorbing properties were calculated by means of transmission line theory. The ZnO/FeNiMo composite has excellent microwave absorption properties of a minimum reflection loss value-27.8 dB at 15.98 GHz for a thickness of 1.5 mm and a broad absorption bandwidth of 13.46–18 GHz（RL 〈-10 dB）.     

Development of Flake Powder Metallurgy in Fabricating Metal Matrix Composites:A Review

Powder metallurgy(PM) is one of the most applied processes in the fabrication of metal matrix composites(MMCs). Recently, a novel PM strategy called flake PM was developed to fabricate MMCs with nano-laminated or hierarchical architectures. The name ‘‘flake PM' was derived from the use of flake metal powders, which could benefit the uniform dispersion of reinforcements in the metal matrices and thus result in balanced strength and ductility. Flake PM has been proved to be successful in the dispersion of nano aluminum oxides, carbon nanotubes, graphene nano-sheets, and microsized B4 C particles in aluminum or copper matrix. This paper reviews the technique and mechanism developments of flake PM in previous studies, and foresees the future develop of this new fabricating method.