Effect of Dy doping on magnetostrictive and mechanical properties of Fe83Ga17 alloy

Fe83Ga17 alloy is a kind of promising magnetostrictive alloys with high magnetostrictive properties and a low saturation magnetic field.As-cast Fe83Ga17 Dyx(x=0,0.05,0.1,0.2,0.4)polycrystalline alloys were prepared by arc melting.Effect of Dy doping on the microstructure,magnetostrictive and mechanical properties of as-cast Fe83Ga17 alloy was investigated.Results show that Dy-doped alloys exhibit a dual-phase structure containing the A2 matrix and Dy-rich precipitates(Fe56Ga34Dy10).Both magnetostriction and mechanical properties of Fe83Ga17 alloys are improved by Dy doping.A small amount of Dy addition(x=0.2)significantly causes Fe83Ga17 alloy to transform from typical brittle material(fracture strainε<1%)to plastic material(ε≈11%).Correspondingly,the fracture mode transforms from intergranular fracture to dimple fracture.At the same time,the ultimate tensile strength and the magnetostriction rise up to 209 MPa and 64 ppm,respectively.Dy-rich precipitates disperse along the grain boundries and inside the grains,which plays an important role in the grain refinement and solution strengthening,and therefore,contribute to the enhancement of mechanical properties of the alloy.The improvement of magnetostriction could be attributed to the large lattice distortion induced by Dy atoms entering into the A2 matrix.Doping Dy into Fe-Ga alloys provides an effective solution to the brittleness in their applications.

Simulation and experimental research on extra-squeeze forming method during gradient sand molding

The flexible extrusion forming process (FEFP) is a sand mold patternless manufacturing technology that enables digital near-net shaping of complex sand molds. But, it is difficult to achieve the gradient sand molds with high surface strength and strong interior permeability by FEFP. To solve this problem, an extra-squeeze forming method based on FEFP for gradient sand mold was developed. To further reveal the extra-squeeze forming mechanism, based on the Johnson-Kendall-Roberts (JKR) theory and “gluing” notions, the single and double-sided squeeze models of gradient sand molds were established using the EDEM software. The squeezing processes of sand molds with different cavity depths of 60, 100, 140, 180, and 220 mm were systemically studied under single and double-sided squeeze conditions. The variation in the void fraction of sand mold as also investigated at a variety of extra-squeeze distances of 2, 3, 4, 5, and 6 mm, respectively. Simulation and test results show that a deeper cavity depth weakens the extrusion force transmission, which leads to a decrease in strength. The sand mold permeability and void fraction are identified to be positively correlated, while the tensile strength and void fraction appear to be negatively correlated. The void fraction of sand molds decreases with a longer extra-squeeze distance. A 6 mm extra-squeeze distance for the sand mold with 220 mm cavity depth results in a 26.8% increase in tensile strength with only a 5.7% reduction in the permeability. Hence, the extra- squeeze forming method can improve the quality of the sand mold by producing a gradient sand mold with high surface strength and strong interior permeability.

Impact of diesel emission fluid soaking on the performance of Cu-zeolite catalysts for diesel NH3-SCR systems

Diesel emission fluid （DEF） soaking and urea deposits on selective catalytic reduction （SCR） catalysts are critical issues for real diesel engine NH3-SCR systems. To investigate the impact of DEF soaking and urea deposits on SCR catalyst performance, fresh Cu-zeolite catalyst samples were drilled from a full-size SCR catalyst. Those samples were impregnated with DEF solutions and subsequently hydrothermally treated to simulate DEF soaking and urea deposits on real SCR catalysts during diesel engine operations. Their SCR performance was then evaluated in a flow reactor with a four-step test protocol. Test results show that the DEF soaking leached some Cu from the SCR catalysts and slightly reduced their Cu loadings. The loss of Cu and associated metal sites on the catalysts weakened their catalytic oxidation abilities and caused lower NO/NI-I3 oxidation and lower high-temperature N20 selectivity. Lower Cu loading also made the catalysts less active to the decomposition of surface ammonium nitrates and decreased low-temperature N20 selectivity. Cu loss during DEF impregnation released more acid sites on the surface of the catalysts and increased their acidities, and more NH3 was able to be adsorbed and involved in SCR reactions at medium and high temperatures. Due to lower NH3 oxidation and higher NH3 storage, the DEF-impregnated SCR catalyst samples showed higher NOx conversion above 400 ℃ compared with the non-soaked one. The negative impact of urea deposits during DEF impregnation was not clearly observed, because the high-temperature hydrothermal treatment helped to remove the urea deposits.

Tailoring magnetostriction and magnetic domains of <100>-oriented Fe80Ga16Al4 alloy by magnetic field annealing

Magnetic field annealing(MFA) was used to tailor the magnetostriction and magnetic domains of Fe80Ga16Al4 alloy,and the relationship between the two characteristics was studied.The <100>-oriented alloy was prepared by the directional solidification technique and annealed for 20 min at 700℃ in a magnetic field of 250 mT along a direction 45 ° to the <100> orientation,followed by furnace cooling in the same magnetic field.The magnetostriction along the length direction(λ‖),the width direction(λ丄) and the saturation magnetostriction(λs) was changed from λ‖=208 × 10^(-6) and λ丄=-16 × 10^(-6) of the initial alloy to λ‖≈λ丄≈ 1/2 λs ≈ 112 × 10^(-6)after MFA.The magnetic domain structure,which mainly refers to the number,size,and direction of the domains,was tailored and rearranged by MFA.This rearrangement of the magnetic domain structure resulted in a shift of magnetostrictive properties parallel and perpendicular to the <100> orientation for the Fe80Ga16A14 alloy.This magnetic field annealing method can aid understanding of the relationship between the microscopic magnetic domains and the macroscopic magnetostrictive properties.It can also aid in further tailoring better magnetostrictive properties within magnetostrictive materials to meet the requirements of different application conditions.

Emission characteristics of flue gas during the chemical-looping combustion process for multi-component solid waste

Solid waste has interactions with its flue-gas products during combustion,which offers the possibility of regulating its pollutant emissions.Especially,these interaction pathways would be clearer under anaerobic conditions when the chemical-looping combus-tion(CLC)process is used.The CLC experiments of multi-component solid waste were conducted on a homemade twin-bed reactor and the characteristics of flue gas were investigated for the effect of the mixing ratio of sewage sludge and polyvinyl chloride(PVC).The results indicated that the combustion efficiency was>99.9%for these CLC processes;the highest carbon-conversion rate was obtained at 96.3%for PVC with 60%sludge.The highest NO and SO_(2)emissions were 26%and 19%,respectively,when the sludge was mixed with 20%PVC.As the proportion of PVC blended into the sludge increased,the time when the concentration of NO in the flue-gas peaks moved backwards,while peak SO_(2)concentration moved forward.The general trend was to increase first and then de-crease.In addition,there were multiple peaks in carbon emissions,corresponding to~10%,30%and~70%of the carbon-conversion rate;nitrogen emissions reached 90%of total emissions before the carbon-conversion rate was 40%;sulphur emissions had a longer cycle and were mainly emitted between 10%and 60%of the carbon-conversion rate.The results are expected to provide a reference for solid-waste source suppressing to inhibit the generation of pollutants.