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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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     

Influences of stoichiometric ratio B/A on structures and electrochemical behaviors of Lao.75Mg0.25Ni3.5Mx （M=Ni,Co; x=0-0.6） hydrogen storage alloys

In order to investigate the influences of the stoichiometric ratio ofB/A （A： gross A-site elements, B： gross B-site elements） and the substitution of Co for Ni on the structures and electrochemical performances of the AB3.5-4.1-type electrode alloys, the La-Mg-Ni-Co system La0.75Mg0.25Ni3.5Mx （M=Ni, Co; x= 0, 0.2, 0.4, 0.6） alloys were prepared by induction melting in a helium atmosphere. The structures and electrochemical performances of the alloys were systemically measured. The results show that the structures and electrochemical performances of the alloys are closely relevant to the B/A ratio. All the alloys exhibit a multiphase structure, including two major phases, （La, Mg）2Ni7 and LaNis, and a residual phase LaNi2, and with rising ratio B/A, the （La,Mg）2Ni7 phase decreases and the LaNi5 phase increases significantly. When ratio B/A-3.7, the alloys obtain the maximum discharge capacities. The high rate discharge（HRD） capability of the alloy （M=Ni） monotonously rises with growing B/A ratio, but that of the alloy （M=Co） first mounts up then declines. The cycle stability of the alloy （M-Co） monotonously increases with rising B/A ratio, but it first decreases slightly then increases for the alloy （M=Ni）. The discharge potential of the alloy （M=Ni） declines with increasing B/A ratio （x〉0.2）, but for the alloy （M-Co）, the result is contrary. The substitution of Co for Ni significantly ameliorates the electrochemical performances. For a fixed ratio B/A=3.7, the Co substitution enhances the discharge capacity from 365.7 to 401.8 mA.h/g, the capacity retention ratio （S100） after 100 charging-discharging cycles from 50.32% to 53.26% and the HRD from 88.65% to 90.69%.     

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）.     

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.     

Microstructure and properties of A1-Cu-Mg-Ag alloy exposed at 200℃ with and without stress

The effect of stress on the microstructure and properties of an Al-Cu-Mg-Ag alloy under-aged at 165℃ for 2 h during thermal exposure at 200℃ was investigated. The tensile experimental results show that the remained tensile strength of both specimens at room temperature after being exposed at 200℃ with and without applying stress rises firstly, and then drops with the increasing of exposure time. The peak value of the remained strength reaches 439 MPa for non-stress-exposure for l0 h, and 454 MPa after being exposed with stress loaded for 20 h at 220 MPa. The elongation change is similar to that of strength. After being exposed for 100 h, specimen exposed at 220 MPa still remains a tensile strength of 401 MPa, larger than that exposed without applying stress. TEM shows that the microstructure of under-aged alloy is dominated by Ω phase mainly and a little θ＇ phase. The θ and Ω phases are believed competitive with increasing exposure time. The width of precipitation free zone（PFZ） increases and the granular second phase precipitates at grain-boundary correspondingly. It is shown that the mechanical properties of alloy decrease slightly and present good thermal stability after thermal exposure at 200 ℃ and 220 MPa for 100 h.     

Effects of vibration and grain refiner on microstructure of semisolid slurry of hypoeutectic Al-Si alloy

The effects of vibration and grain refiner on the microstructure of semisolid slurry of hypoeutectic Al-Si alloy were studied. The impact of vibration on the convection of liquid was conducted by using a system of water-particle tracer. The 356 melt at temperature of 630-660 ℃ with or without grain refiner Al-5%Ti-1%B was poured into a metal cup as the vibrating vessel, then it was cooled to 590-610 ℃ in the semisolid zone and kept for some time, subsequently vibration with different frequencies was applied. The results show that the primary a（Al） particles become finer and rounder with the increase of vibration frequency. The slurry with primary a（Al） equivalent particle diameter（EPD） of about 90μm and average shape coefficient（ASC） of about 0.5 can be prepared under vibration of 20 Hz. With the combined action of vibration and grain refiner Al-5Ti-B, even smaller and rounder spheroids with EPD of about 85μm and ASC of about 0.6 are obtained.     

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.     

Effect of H_2 Reduction Temperature on the Properties of Reduced Graphene Oxide and Copper Matrix Composites

Reduced graphene oxide(RGO) and copper composites(RGO/Cu) were successfully fabricated based on a molecular-level mixing method(MLM). The composite powders were reduced in H2 at 350, 450, and 550 °C and then consolidated by spark plasma sintering(SPS) in order to evaluate the effect of H2 reduction temperature on the properties of the composites. The results indicate that the strengths of the composite decrease with the increase of H2 reduction temperature, while the electrical conductivity reaches its maximum at 450 °C and minimum at 550 °C. Hot rolling could benefit the electrical conductivity. The yield strength of the RGO/Cu composite reduced to 337 MPa at 350 °C. The electrical conductivity of the RGO/Cu composite reduced at 450 °C after hot rolling reaches 60.26% IACS. The properties of the RGO/Cu composites can be designed by adjusting the reduction degree of RGO and by hot rolling.