Abstract: A physicometallurgical model of flow stress, recovery, recrystallization and precipitation was developed to simultaneous-ly calculate the change in dislocation density, the nucleation and growth of recrystallized grains and the carbonitride precipitation of steel during hot rolling. The agreement of the laboratory simulation results by this model with experimental data indicates that the volume fraction of recrystallization and the grain size of niobium-containing micro-alloyed steel can be predicted with the model in different hot rolling processes. The model contains essential description of the observed metallurgical phenomena, and can be in principle adapted to different kinds of alloyed steels by changing some basic constants of materials.
Abstract: Metal surfaces were treated by silane, phosphate and untreated respectively, and then adhered by epoxy resin. The mechanical properties of the adhesive joints by different treatment methods were investigated and the effect of surface treatment on the fatigue performance of the adhesive/metal interface was analyzed. The stress-strain curves of the adhesive joints were compared before and after fatigue load was applied on the joints. Crack propagation in the interface was discussed on the basis of fracture mechanics. The results show that the fatigue resistance of silane-treated samples is the best and the adhesive strength is the greatest. Adhesion failure always initiates at the interface. Energy can release through propagation of crack tips and also can through plastic deformation of the adhesive layer.
Abstract: Galvanic protection distance (PD) and the effect of the addition of various contents of Cl- on it were studied with galvanized auto steel sheet specimens whose zinc coating was partly removed and covered with Ying-tan soil mud. The results show that in the mud without Cl- the PD value increase linearly with the thickness of mud layer, and the red-rust emerging time increases correspondingly. With increasing Cl- content and thickness of covered mud, the PD value raises and reaches a maximum. Cl- content influences not only the average corrosion current density, but also the dissolved oxygen, pH value and electrical conductivity. The thickness of mud layer and Cl- content control the PD value and surface corrosion state.
Abstract: The solidification behavior of Cu100-XFeX(X=15, 20, 30 and 40) alloys was investigated by gas atomization. Considering the common action of minority phase spheres' nucleation, diffusion growth, spatial movement and interaction between solidification interface and minority phase spheres, a model was developed to describe the kinetics of metastable liquid-liquid phase transformation and microstructure evolution in the metastable immiscible alloys with different volume fractions of minority phase spheres. Coupled with the movement, thermal and mass transfers during the atomized droplet flight, the numerical model was resolved. The kinetics of metastable liquid-liquid phase transformation in Cu-based immiscible alloys was investigated by numerical simulation. The results indicate that the average size of Fe-rich spheres increases with the increase of Fe concentration. The nucleation event takes place around the peak of matrix liquid supersaturation. With the increase of cooling rate, the nucleation undercooling and the nucleation rate increase, but the average radius of Fe-rich spheres decreases. The formation of Fe-poor layer on the large powder surface is the result of the common actions of the Fe-rich spheres' Marangoni migration and repulsive interaction between the solid/liquid interface and Fe-rich spheres.
Abstract: The aging precipitation of a Fe-Cu alloy cold-deformed 50% and 80% was studied. Optical microscope and HREM were employed to observe the microstructure and precipitation in thermo-mechanical processing, and the effect of cold deformation on the aging precipitation was analyzed. The results show that cold deformation is helpful to the precipitation of second phase, after a large quantity of cold deformation the precipitation is accelerated and the bulk volume of second phase becomes greater. Copper-rich transition phase is precipitated in advance and then transformed to ε-Cu phase with the increase of time during the overaging period. The copper-rich phase, i.e. GP zone, is the main cause to strengthen the alloy.
Abstract: W powders with rare earth oxide La2O3 were prepared by liquid-solid blending method, which includes mixing La(NO3)3 and WO3, drying, decomposition of La(NO3)3 and reduction of WO3. CuW electrical contact materials with La2O3 were fabricated by powder metallurgy-infiltration technology. The effect of holding time on the revivification of La(NO3)3 and that of La2O3 addition on the properties of CuW electric contact materials were investigated. The results show that La2O3 distributes uniformly in fine tungsten compound powders, and the particle size of powders decomposed by La(NO3)3 increases with prolonging holding time. The electrical breakdown strength of CuW electrical contact materials doped with La2O3 increases significantly.
Abstract: Four experimental multi-component Ni-base superalloys were designed to investigate the influence of high Ru and high Cr on the microstructural stability at high temperature. These alloys were solution-treated and then aged at 800-1 100℃ for 10-1 300 h. The experimental results showed that no TCP phases were found in the Ru-free or Cr-free alloy after aging at 1 000℃ for 1 300 h. For the alloy with high level of Cr addition, TCP phases were observed to precipitate along grain boundaries and in dendrite cores after 20 h and 50 h at 1000℃, respectively; after aging at 1000℃ for 1000 h, no TCP phases were observed in the alloy with high levels of Cr and Ru additions. It is indicated that the high level of Cr addition promotes the precipitation of TCP phases, while high level of Ru addition efficiently lowers the propensity for the formation of TCP phases in the high Cr-containing alloy, and thus improve the microstructural stability.
Abstract: Nickel base powder superalloy Inconel 718 was prepared from pre-alloyed powder by supersolidus liquid phase sintering. The results show that compacts with a relative density over 98% can be obtained by sintering at 1240℃ for 120 min in vacuum. The relative density of sintered samples could be increased to 99.7% by next hot isostatic pressing process. The tensile strength and ductility of heat-treated samples are 1 280 MPa and 9% respectively at room temperature. The precipitates are spherical γ' and needle γ' and coarse carbides, and the average grain size is below 50μm.
Abstract: The effects of Al and W additions on the solidus-liquidus temperature, heat-treated microstructure and hardness of four Co-Al-W ternary alloys were investigated. The results show that the solidus and liquidus temperatures of these Co-Al-W ternary alloys are higher than the liquidus temperatures of Ni-base single crystal superalloys, γ(fcc) single phase existed in the matrix of three alloys after solid solution treatment at 1 300℃ for 8 h, while μ phase-Co7W6 was observed along grain boundaries and in grain interiors in the alloy containing high level of W. γ' phase-Co3 (Al, W) with Ll2 structure precipitated in the γ matrix of four alloys after aging treatments at both 800℃/100 h and 900℃/50 h, similar to the microstructure of Ni-base superalloys. High levels of W and Al addi-tions promoted the precipitation of μ phase-Co7W6 and Al-rich phase, respectively. Combined with the results of hardness after different aging treatments, the composition range of these ternary alloys containing γ + γ' two phases was preliminarily determined based on microstructural stability and potential high-temperature mechanical properties.
Abstract: Powder injection molding (PIM) was used to prepare sintered Sm2Co17 magnets with paraffin wax (PW) based binder, which consists of 70% PW, 10% LEPE, 10% PP, and 10% SA (mass fraction). The binder is removed by thermal debinding in the mixing atmosphere of argon and hydrogen. The magnetic properties of the sintered PIM magnets are remanence Br=0.51 T, intrinsic coercivity Hcj=168 kA·m-1, and maximum energy product BHmax=21.3 kJ·m-3. Compared with commercial magnets, the magnetic properties are poor because the PIM magnets have high carbon mass fraction (0.33%). Carbon consumes the effective content of Zr and forms high melting-point nonmagnetic phase (ZrC), which results in the decrease in volume content of lamella phase and 1:5 phase. Deterioration of the cellular structure and SEM structure leads to the decrease in magnetic properties of the PIM magnets. It is concluded that residual carbon in the magnets should be removed when the sintered magnets is prepared by PIM.
Abstract: Experiments were conducted to investigate the effect of grain refining mechanism on the microstructure and mechanical properties of 1060 commercially pure aluminum in accumulative roll bonding (ARB), in which two kinds of routes, Route A and Route B, were employed. The results show that the effectiveness of Route A is better than Route B. After ARB of 7 passes, the microstructure of the specimen by Route A consists of thin elongated fibriform grains with an average size of 470 nm, but that by Route B does compressed grains with an average size of 680 nm. The improvement in tensile strength by Route A is greater than that by Route B. The strengthening mechanism of 1060 commercially pure aluminum by ARB is fine-grain strengthening. The deformation rule and the formation mechanism of fine grains were analyzed elementarily in ARB process.
Abstract: The microstructure and properties of retrogression and retrogression re-aging (RRA) treated 7B04-T651 Al alloy prestretched thick plates were studied by transmission electron microscopy, MTS-810 test system and conductivity meter. The results show that the appropriate RRA temper with retrogression at 180± 5℃ for 1 -2h can produce the remarkable improvement in electrical conductivity, with only a 2%-5% reduction in strength below T6. TEM observations of RRA samples show that the precipitation is extremely fine and distributed homogeneously inside the grains, being slightly denser and more stable than that resulting from the T6 temper; whilst the grain boundary precipitation is quite different from that resulting from T6 treatment, the particles being coarser, and much closer to the precipitation resulting from T74 temper.
Abstract: A pure Al film was sputtered by DC magnetron on AZ31B magnesium alloy and heat-treated in a high vacuum. It was determined by the analyses of SEM and XRD that the Al film was ultra-fine polycrystalline. The thickness, critical adhesive force, hardness and elastic modulus of the Al film were measured by nano-indentation/scrateh test; the composition profile and properties were tested by glow discharge spectrometry (GDS). The results show that the thickness of the Al film decreases with increasing heat treatment temperature. Compared with the magnesium alloy, the Al film has a higher surface hardness and elastic modulus which decrease with increasing depth. A transition nano-scale layer forms between the Al film and substrate, which is of adherent trait and reveals somewhat elastoplastic property. It is concluded that the magnesium alloy can be protected by the Al film.
Abstract: AZ91 magnesium alloy was fabricated by powder metallurgy. The effects of sintering temperature on the relative density and thermal conductivity were investigated. The microstructure of the material was observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The result shows that the best sintering temperature is 610 12. At this sintering temperature the relative density can reach 97.4% and the highest thermal conductivity can be up to 63.1 W·m-1·K-1. The sintering microstructure of the alloy is composed of α-Mg solid solution matrix and β-Mg17Al12. The β phase exhibits two main forms, i.e., divorced eutectic 13 phase and discontinuous precipitated β phase.
Abstract: The effect of Sr addition on the grain refinement of ZK60 magnesium alloy was investigated by means of OM, SEM and EDX. The results indicate that adding small amounts of Sr can effectively refine the as-cast microstructure of ZK60 alloy, but the effects of Sr adding amount and melt holding time on the refinement efficiency are obvious. For a given melt holding time, the refine-ment efficiency enhances with the Sr adding amount increasing from 0.01% to 0.1%. For a given Sr adding amount, the refinement efficiency enhances with the melt holding time increasing from 20 to 80 min, hut reduces obviously while the melt holding time exceeds 80 min.
Abstract: Two eutectic alloys, AAG1 and AAG2, were selected as solder according to the Ag-Au-Ge ternary phase diagram. The solder alloys were prepared by vacuum melting. The melting point, wettability, microstructure of the solder alloys and the interface between solder and Al-SiC/Ni/Au substrate were investigated. The results show that these two solder alloys have large temperature gap between solidus and liquidus. The temperature of solidus and liquidus are 410.0℃; and 449.8℃ for AAG1 and 401.1℃ and 441.0℃ for AAG2, respectively. The alloy AAG1 has good wettability to the substrate. Both two solder alloys have good adhesion with the substrate. No intermetallic phase was found at the interface. It is concluded that the alloy AAG1 could be possibly used as the solder for 400-500℃.
Abstract: Chemical structures of the specular spin valve with two nano-oxide layers (Ta/Ni80Fe20/Ir19Mn81/Co90Fe10//NOL1//Co90Fe10/Cu/Co90Fe10//NOL2/Ta) were studied by X-ray photoelectron spectroscopy (XPS) and peak decomposition technique. The results show that there are thermodynamically favorable reactions at the CoFe/NOL1 and NOL2/Ta interfaces. The CoFe sense layer remains metallic, and the Ta capping layer near the CoFe sense layer is oxidized to Ta2O5 acting as the NOL2, which is formed through the interface reaction between the oxidized CoFe and the Ta layer. ROLl is a discontinuous oxidation layer because of the existence of some residual metallic CoFe, which allows the direct exchange coupling to exist. Mn atoms of the IrMn layer diffuse into NOL1 during annealing. However, it's further diffusion can be inhibited due to the formation of Mn oxides by the reaction between ROLl and the Mn diffused from IrMn during annealing.
Abstract: SiCp/Al composites with high volume fraction for electronic packaging were prepared by powder injection molding and pressureless infiltration. The effects of the particle size and volume fraction of SiC on the thermophysical properties of SiCp/Al composites were investigated. The results show that thermal conductivity of SiCp/Al composites increases with the increase of the particle size and volume fraction of SiC. The coefficient of thermal expansion (CTE) of the composites is not affected by the particle size of SiC but depends on the volume fraction of SiC. With the increase in volume fraction of SiC the CTE of the composites decreases, and it agrees well with the predicted values based on Turner's model. By graduation of SiC particles with different sizes, it can be realized that the volume fraction ranges from 53% to 68%. As a result, the CTE(20-100℃) of the composites changes from 7.8×10-6 to 5.4×10-6 K-1, and thermal conductivity from 140 to 190 W·m·K-1.
Abstract: Silicon carbide (SIC) ceramics with submicron silicon carbide as raw material and Al2O3 and Y2O3 as sintering additives were fabricated by spark plasma sintering (SPS). The densification process of the materials was analyzed, and the effects of sintering temperature, sintering pressure and time on the densification and mechanical properties were investigated. It is found that the SiC with a relative density of 99.1% can be achieved when the sintering temperature, sintering pressure and holding time are 1 600℃, 50 MPa and 5 min, respectively. The mechanical properties of the sintered SiC are HV 2550 in hardness, 8.34 MPa·m1/2 in fracture toughness and 684 MPa in bending strength.
Abstract: SrTiO3 in which Sr2+ is included was solidified by self-propagation high-temperature synthesis (SHS). Some influential factors on the solid dendification were analyzed by experiment. The optimal process parameters for preparing SrTiO3 and composites were determined as the following:the preform density of 56%; the pre-pressure of 10 MPa, the pressing time of 4 s; the high pressure of 300 MPa, the dwell time of 8 s under high pressure.
Abstract: The effects of artificial weathering on the chemical structure, surface topography and mechanical properties of ethylenepropylene-diene monomer (EPDM) were investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), computer-controlled testing machine and spectrophotometer. The results showed that an oxidation layer formed after 90 d of exposure. XPS results confirmed the production of C-O-C/C-OH, C=O and O-C=O groups. With prolonging exposure time, the crosslink density increased linearly, the surface of EPDM turned to redder, more yellow and lighter. Little voids and micro cracks were formed under exposure to artificial weathering environment. The tensile strength, tear strength and hardness increased with prolonging exposure time.
Abstract: Micro powder injection molding (μ-PIM) was studied to manufacture micro-sized gearwheels of iron. Carbonyl Fe powder with a mean size of 2.3 μm and wax-based thermoplastic binder mixture were used in the manufacture process. When the powder loading was fixed as 58%, the molded compact of a gearwheel whose addendum circle diameter is 700 μm was obtained with well shape retention. The profile of the gearwheel and the roundness of the centre hole were kept well after sintering. The sintering shrinkage of the addendum circle is 15.6% and the roughness of the gearwheel surface is Sa=5.099 μm.
Abstract: Theoretical flame temperature is considered as one of the important parameters which reflect the thermal state of a hearth. A new model with the detailed explanation of each parameter was presented for calculating the theoretical flame temperature. Based on this model, a computer program was developed in order to calculate easily. The calculation results of theoretical flame temperature show that compared with traditional models the new model can reflect the thermalt sate of a hearth more effeetively.
Abstract: In combination of genetic algorithm with BP network, a new intelligent PID control algorithm was designed using genetic algorithm to optimize the parameters of BP neural network, which improve the dynamic performance of a temperature control system. The temperature control system model of a dieless drawing system was fitted with collected experimental data. Simulation results show that the proposed model has a better rapidity and robustness.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
