Evaluation of fatigue life of AZ31 magnesium alloy fabricated by squeeze casting

Cyclic deformation behavior and fatigue life of squeeze-cast AZ31 magnesium alloy was studied under stress amplitude-control at room temperature. Low and high cycle fatigue tests with engineering stress amplitudes in the range from 40 to 110 MPa were conducted. Analysis of hysteresis curves was performed. Tension–compression asymmetry of hysteresis loops was not observed; the alloy exhibited cyclic hardening in tension and compression. The fatigue life in the low cycle fatigue region was expressed by Wöhler and derived Manson–Coffin curves. Experimental data in both, the low and high cycle fatigue regions were fitted by means of regression functions. S–N curves exhibited a smooth transition from the low to the high cycle fatigue regions and significant scattering of experimental points was observed. Furthermore, metallographic and fractographic analyses were performed. Crack initiation occurred from the specimen surface or on clusters of secondary particles; the region of final fracture was characterized by a transgranular ductile fracture.It can be concluded that the fatigue properties of squeeze cast magnesium alloy AZ31 are significantly improved comparing to materials prepared by common methods of casting. Squeeze casting also enables the cost-effective fabrication of complicatedly shaped parts.     

Anisotropic thermal expansion behavior in tetragonal Sr2MgWO6

The colorless sample of Sr₂MgWO₆ was prepared by conventional solid-state reaction of stoichiometric amounts of SrCO₃, WO₃ and MgO and characterized by powder X-ray diffraction (XRD) studies. In the temperature range of 300–15 K, detailed structural studies on Sr₂MgWO₆ were carried out by Rietveld refinements of the observed powder neutron diffraction (ND) data. At ambient temperature Sr₂MgWO₆ crystallizes in tetragonal (space group I4/m) lattice with unit cell parameters: a = 5.5882(2) and c = 7.9452(7) Å, V = 248.11(3) Å³, Z = 2. This tetragonal (I4/m) structure is retained down to 15 K. The structural analysis of the sample at different temperatures indicates no appreciable change in the MgO and WO bond lengths. However, a decrease in the tilt angle is observed with increasing temperature. The negative thermal expansion of the c-axis is attributed to increasing transverse displacement amplitude of the bridging oxygen atoms along this axis.     

Enhanced photoluminescence and electrical properties of 0-3 type ZnO/Bi3.6Eu0.4Ti3O12 nanocomposite thin films

0-3 type ZnO/Bi_3.6Eu_0.4Ti₃O₁₂ (BEuT) nanocomposite films with ZnO nanopowders in BEuT host were prepared by chemical solution deposition. The effects of ZnO content on the structure, photoluminescence, and electrical properties of the films were investigated. The ZnO/BEuT molar ratio strongly affected the grain size and growth orientation of BEuT, dielectric and ferroelectric properties, as well as emission intensity. The nanocomposite films showed strong red emission peaks due to ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions of Eu³⁺ ions. Good electrical properties with high dielectric constant of 480 (at 1 kHz) and large remanent polarization (2P_r) of 32 μC/cm² were obtained for the nanocomposite films having a ZnO/BEuT molar ratio of 1:2. The mechanisms for enhanced photoluminescence and electric properties were discussed. The results suggest that the nanocomposite thin films are promising candidate materials for multifunctional optoelectronic devices.     

德胜川钢钒钛精矿烧结配矿试验研究

针对四川德胜集团钢铁有限公司烧结厂使用较高比例的钒钛磁铁精矿的烧结生产情况,通过实验室烧结杯试验,研究了钒钛磁铁精矿配比和碱度对烧结矿烧结性能的影响。研究结果表明:在目前德胜钢铁有限公司的原、燃料和配矿结构条件下,要保证烧结矿产质量、节能和降低原料成本,合适的钒钛磁铁精矿配比为45%,合适的碱度为2.3。     

Plastic deformation behaviors of a Mg–Ce–Zn–Zr alloy

The stress–strain behaviors of a Mg–2.8%Ce–0.7%Zn–0.7%Zr (wt.%) alloy with various strain rates at different deformation temperatures were investigated. It is found that the alloy can be extruded at 623 K with σ_0.2=222.4 MPa, σ_b=257.8 MPa and δ=12.0%. The working hardening, the dynamic recovery and the dynamic recrystallization play important roles to affect the plastic deformation behaviors of the alloy at different temperature regions, respectively.     

A nest-like hierarchical porous V2O5 as a high-performance cathode material for Li-ion batteries

In this article, V₂O₅ with a novel nest-like hierarchical porous structure has been synthesized by a facile solvothermal method and investigated as cathode material for lithium-ion batteries. The nest-like V₂O₅ with a diameter of about 1.5 µm, was composed of interconnected nanosheets with a highly porous structure. Without other modification, the as-prepared V₂O₅ electrode exhibited superior capacity. An initial discharge capacity of 330 mAh g⁻¹ (at a current density of 100 mA g⁻¹) could be delivered and a stable discharge capacity of 240 mAh g⁻¹ after 50 cycles is maintained. The excellent performance was attributed to the hierarchical porous structure that could buffer against the local volume change and shorten the lithium-ions diffusion distance.     

Achievement of high electric performances for bismuth titanate-based piezoceramics via hot press sintering

Bi₄Ti₃O₁₂ (BIT) ceramic has great potential in high-temperature environment due to its high Curie temperature T_C ~ 675 °C. In this work, hot press sintering (HPS) is applied on the 0.01 mol Ce and Nb/Cr co-doped BIT (BCTNC) ceramics to enhancing the low piezoelectric coefficient (d₃₃ < 7 pC/N) and resistivity. Extremely high d₃₃ (~39 pC/N) together with high T_C (~672 °C) and high dc resistivity ρ (~1.49 ×10⁷ Ω?cm at 500 °C) are obtained in HPS samples. The enhancement of piezoelectricity benefits from high density of domain and high poling electric field. Moreover, outstanding thermal stability of piezoelectric constant (d₃₃ ~ 35 pC/N after annealing at 650 °C) and low dielectric loss (tanδ ~ 3.8% at 500 °C) are observed as well. These findings are instrumental in understanding HPS and provide a possible manipulation of crystallized mechanism and domains growing kinetics to enhance piezoelectric performances of BIT based ceramics.     

三种高Sn无铅钎料的表面张力和润湿性能研究

采用悬滴法测量了3种无铅钎料合金(Sn-3.0Ag-0.5Cu、Sn-0.7Cu与Sn-9.0Zn)在260℃时的表面张力,分别为525.5,534.8和595.4 mN/m;同时采用座滴法测量了其在260℃熔融状态下与Cu基板的接触角,分别为24.5°、28.0°和102.5°,并且与传统Sn-37.0Pb钎料进行了比较研究。结果表明,无铅钎料合金的表面张力与接触角均大于Sn-37.0Pb钎料。结合Young-Dupre公式讨论了钎料合金表面张力与其润湿性能的相关性,认为Sn基钎料合金在Cu基板上的润湿性能主要取决于其表面张力。