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.     

Oxidation ofAl2O3-dispersion chromizing coating by pack-cementation at 800 ℃

Preparation and oxidation of an Al2O3-dispersed chromizing coating were investigated by chromizing an aselectrodeposited Ni-Al2O3 nanocomposite film using a conventional pack-cementation method at a greatly decreased temperature （800 ℃）. For comparison, chromizing was also performed with the same condition on an as-deposited Ni film without Al2O3 nanoparticles. Oxidation at 900 ℃ indicates that, compared with the Al2O3-free chromizing coating, the Al2O3-dispersed chromizing coating exhibits a increased oxidation resistance, due to the formation of purer and denser chromia scale. The effect of Al2O3 on the coating formation and the coating oxidation behavior was discussed in details.     

Effect of Cr Content on the Compression Properties and Abrasive Wear Behavior of the High-Volume Fraction(TiC–TiB_2)/Cu Composites

The(TiC–TiB2)/Cu composites with 50 vol% Ti C–Ti B2 ceramic particles were successfully fabricated by the combustion synthesis and hot press consolidation in a Cu–Ti–B4C–Cr system. The effects of the Cr content on the microstructures, hardness, compression properties, and abrasive wear behaviors of the composites were investigated. The final products consist of only Cu, Ti C, and Ti B2 phases, and the ceramic particles are distributed uniformly in these composites. The size of the ceramic particles decreases with Cr addition. As the Cr content increases, the yield strength,ultimate compression strength, microhardness, and abrasive wear resistance of the composites increase, and the fracture strain decreases.     

Friction Stir Welding of Discontinuously Reinforced Aluminum Matrix Composites:A Review

Friction stir welding(FSW) is considered a promising welding technique for joining the aluminum matrix composites(AMCs) to avoid the drawbacks of the fusion welding. High joint efficiencies of 60%–100% could be obtained in the FSW joints of AMCs. However, due to the existence of hard reinforcing particles in the AMCs, the wearing of welding tool during FSW is an unavoidable problem. Moreover, the low ductility of the AMCs limits the welding process window. As the hard materials such as Ferro-Titanit alloy, cermet, and WC/Co were applied to produce the welding tools,the wearing of the tools was significantly reduced and the sound joints could be achieved at high welding speed for the AMCs with low reinforcement volume fraction. In this article, current state of understanding and development of welding tool wearing and FSW parameters of AMCs are viewed. Furthermore, the factors affecting the microstructure and mechanical properties of the joints are evaluated in detail.     

Effects of Reheating Duration on the Microstructures and Tensile Properties of Thixoforged In Situ Mg_2Si_p/AM60B Composites

The influences of reheating duration on microstructures and tensile properties of thixoforged in situ Mg2Sip/AM60 B composites have been investigated. The results indicate that the reheating time affects the volume fraction,composition and distribution of the liquid phase, the evolution of the liquid pools within the primary particles, and the morphology and distribution of the Mg2 Si particles of the semisolid feedstock. These changes then affect the subsequent solidification behavior and deformation mechanism during thixoforging, which are responsible for the resulting microstructure and tensile properties. Mg2 Si particles play a strengthening role for the matrix through the load transfer mechanism. The appropriate reheating time is 60 min at 600 °C when the mold preheating temperature is at 300 °C. The ultimate tensile strength and elongation of the resulting composite are up to 209 MPa and 11.9%, respectively.     

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.     

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.     

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.     

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.     

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.     

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 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.     

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）.     

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.     

Effect of second introduced phase on magnetotransport properties of La2/3Sr1/3MnO3/0.33（CuO,ZnO, Al2O3） composites

The structure, magnetic and magnetotransport properties of La2/3Sr1/3MnO3（LSMO）/0.33（CuO, ZnO, Al2O3） composites were investigated to explore the role of second introduced phase. The microstructural analysis shows two kinds of grain boundaries： LSMO/LSMO and LSMO/second phase/LSMO. Two maximal resistivities appear in LSMO/0.33CuO and LSMO/0.33ZnO composites while the resistivity of LSMO/0.33Al2O3 decreases monotonically with increasing the temperature from 200 K to 400 K. Moreover, the temperature dependence of magnetoresistance（MR） of LSMO/0.33A1203 that decreases monotonically with increasing the temperature is different from that of LSMO/0.33CuO and LSMO/0.33ZnO. A developed two-channel model consisting of scattering model and tunneling model was proposed to fit the resistivity—temperature curves of these composites. The role of second introduced phase and the magnetotransport mechanism of these composites were elucidated.