Microstructural evolution in adiabatic shear bands in Ta and Ta–W alloys

Microstructural evolution of adiabatic shear bands originated due to high strain, high strain rate deformation in Ta and Ta–W alloys has been examined. Tests were performed using a specially designed stepped specimen in a Hopkinson bar. Upon completion of the deformation, the region is cooled to below one half of the temperature achieved during adiabatic heating in less than one millisecond. Microstructural characterization of the shear bands was performed using optical microscopy as well as scanning and transmission electron microscopy. No evidence of recrystallization within the shear bands could be found. This is in contradiction with several recent reports, which claim that recrystallization may take place at these stringent time and temperature conditions. These studies, however, do not take into account the kinetics of boundary refinement processes, which are a distinctive characteristic of a recrystallized microstructure. It will be shown that the absence of recrystallization in Ta and Ta–W adiabatic shear bands can be predicted by a progressive subgrain misorientation (PriSM) recrystallization model, applied successfully in previous studies to predict the microstructure evolution in copper adiabatic shear bands.     

The wear resistance of Ni alumina and NiAl2O4 alumina nanocomposites

The influence of metallic Ni or NiAl₂O₄ as a reinforcing particle on grain growth and wear resistance in alumina matrix composites was evaluated. Alumina composites with various Ni or NiAl₂O₄ concentrations were prepared by multiple-infiltrations of Ni-nitrate into bisque-fired (necked) alumina green bodies followed by heat treatment and sintering at 1600 °C for 2 h. Sintering in a reducing environment resulted in composites with metallic Ni nanoparticles, while NiAl₂O₄ alumina composites were formed when sintering in air. The addition of Ni or NiAl₂O₄ resulted in a reduction in alumina grain size after sintering. The material response to abrasive wear was estimated by measuring the time to section samples of a defined area using a diamond wafering saw and was compared to the wear resistance of undoped alumina. In both cases, reinforcing alumina with Ni or NiAl₂O₄ particles resulted in a significant increase in wear resistance, correlated to the reduced grain size.     

BP神经网络在高炉铁水硅预报中的应用

随着现代科技的发展和计算机技术的不断提高,高炉自动化操作显得越来越重要。高炉铁水硅预报能很好地反映高炉内热状态和高炉的成分,对高炉运行状态的判断起到至关重要的作用。在总结前人预报模型的基础上,综合考虑了各种影响因素,建立了BP神经网络模型,并结合现场数据进行计算,模拟结果和实际相符。     

Influence of Extrusion Joint on Microstructural Evolution and Properties of Mg Alloy Sheet

The mechanical behaviour of AZ31 magnesium alloy sheet with the extrusion joint(EJ) was evaluated.Extruded joint of AZ31 alloy sheets was obtained by the hot extrusion process. Tensile tests were carried out along the extrusion direction at room temperature, and both the non-uniform plastic deformation and the fracture behaviour were studied. It is found that the samples with EJ present significantly deteriorated mechanical properties compared with the EJfree counterpart. Inhomogeneous microstructure distribution around EJ zone brings in the uncoordinated deformation due to the high density of f10"12g twins which were readily activated during plastic deformation.     

Glass like behaviour in Pb(Mg1/4Cd1/12Nb2/3)O3 relaxor

Single phase perovskite ceramic Pb(Mg_1/4Cd_1/12Nb_2/3)O₃ (PMCN) was prepared by the high temperature solid-state reaction method. Dielectric constant and loss tangent were measured over a frequency range 1 kHz–1 MHz in the temperature region −50 –115 °C. Dielectric studies revealed the relaxor behaviour with diffuse phase transition. The frequency dependence of the temperature of the permittivity maximum (T_m′) has been modeled using Vogel–Fulcher relation. The dielectric relaxation in PMCN is found to be analogous to the magnetic relaxation in spin-glass system.     

Effect of Composition on Desulfurization Capacity in the CaO-SiO2-Al2O3-MgO-CaF2-BaO System

The desulfurization capacities of CaO-SiO₂-Al₂O₃-MgO-CaF₂-BaO complex flux were determined experimentally at 1873 K (1600 °C), and the effects of composition on desulfurization abilities were analyzed using the method of quadratic orthogonal regression. The results suggested that the desulfurization rate decreased with an increasing ratio of Al₂O₃/CaO, and the addition of BaO and MgO to the flux improved the desulfurization capability. The increase of the CaF₂ content improved the desulfurization effect for high MgO contents or BaO contents bearing slags.     

Effect of composition on the crystallisation behaviour of blast furnace slag using single hot thermocouple technique

When the content of glass in blast furnace slag is over 95%, it can be used as a raw material in the manufacture of cement. The critical cooling rate required for the formation of glassy slag is one of the important characteristics for molten BF slag. The crystallisation behaviour of molten BF slag has been studied by in situ observation with the single hot thermocouple technique. The isothermal and non-isothermal experiments were performed to construct time–temperature-transformation and continuous-cooling-transformation diagrams. The effect of MgO, Al₂O₃ and binary basicity (CaO/SiO₂) on the critical cooling rate of the CaO–SiO₂–MgO–Al₂O₃ slags were studied under conditions of CaO/SiO₂?=?1.1–1.4, 6–12?mass% MgO and 10–16?mass% Al₂O₃. The following finding are reported in the present paper: (i) Higher MgO content increased the critical cooling rate; higher Al₂O₃ content decreased the critical cooling rate; higher CaO/SiO₂ increased the critical cooling rate. (ii) The crystallisation temperature of molten BF slag lowers as the cooling rate increases, the slag have larger critical cooling rate, higher crystallisation temperature. The results could be used to design proper cooling path of molten BF slag for the formation of glassy.     

Influence of internal stresses in superplastic joining of zirconia toughened alumina

Joints between various compositions of 3 mol% Y₂O₃-stabilized ZrO₂/Al₂O₃ composites have been produced by superplastic flow at 1350 °C and strain rates of 1×10⁻⁵ s⁻¹. The joints are pore free and Vickers indentation induced cracks indicate that the joints are strong. The cracks have been used to measure residual stresses, which can be modified by using an interlayer between the materials to be joined. The results agree well with those obtained by finite-element analysis. Ruby fluorescence has been used to measure the hydrostatic stress.     

Processing of vanadium: a review

Vanadium is an important by-product that is used almost exclusively in ferrous and non-ferrous alloys due to its physical properties such as high tensile strength, hardness, and fatique resistance. Vanadium consumption in the iron and steel industry represents about 85% of the vanadium-bearing products produced worldwide. The ubiquitous vanadium is employed in a wide range of alloys in combination with iron, titanium, nickel, aluminum, chromium, and other metals for a diverse range of commercial applications extending from train rails, tool steels, catalysts, to aerospace. The global supply of vanadium originates from primary sources such as ore feedstock, concentrates, metallurgical slags, and petroleum residues. Vanadium-bearing host minerals consist of carnotite, mottramite, patronite, roscoelite, and vanadinite. Deposits of titaniferous magnetite, uraniferous sandstone, bauxite, phosphate rock, crude oils, oil shale and tar sands host vanadium. Apart from titanomagnetite and ilmenite ore deposits containing vanadium, slags from the ferrous industry are a major source of supply. At present, known world reserves are expected to supply the next century’s needs. Vanadium-bearing materials are treated by means of several processes such as calcium reduction, roast/leach, solvent extraction and ion exchange to recover vanadium either as metal, ferrovanadium, vanadium pentoxide, or in the form of various chemicals. The recovery of aluminum and magnesium metal from smelters and refineries generates vanadium and associated compounds. Countries such as China, South Africa, and Russia are the largest world producers of ferrovanadium and its toxic oxides while about 40 other countries contribute smaller quantities in different forms for global consumption. Australia is poised to become a major player for this essential substance during the next decade. The supply and demand of vanadium products during the past 20 years has been relatively stable and subject to a gradual decline in delivered price. The paper describes established industrial processes for recovery of vanadium from sources such as raw ore and process reverts. The comprehensive condensation of pertinent facts is intended to provide a single reference source rather than the reader perusing many articles.