Structural and mechanical properties in AA 5083 processed by ECAE

Abstract

Equal channel angular extrusion has been used to analyse refining of grains in an industrial 5083 aluminium alloy during severe plastic deformation. The influence of the total strain as well as of the processing route were studied by tensile tests and TEM. The room temperature behaviour and the high temperature properties suggest that large strains increase the density of high angle boundaries in the material. The optimal processing route to achieve grain refinement appears to be route B for the present investigation.     

蜂窝增强泡沫塑料的静动态力学性能

采用蜂窝切割和注塑成型两道工序制备了蜂窝增强泡沫塑料试样, 并对试样进行了准静态压缩试验。通过试验机压头的压力-位移数据, 计算不同参数蜂窝增强泡沫塑料试样的应力-应变曲线。实验结果表明, 在相同条件下, 所有蜂窝增强泡沫塑料试样的应力均大于蜂窝与泡沫塑料的应力之和。通过分析得出, 随着蜂窝孔格边长的减小和试样厚度的增大, 复合效应更加明显。在此基础上, 建立了蜂窝增强泡沫塑料的仿真模型, 并对模型施加压力脉冲载荷, 验证了复合材料在动态冲击下, 同样具有良好的复合效应。研究表明, 这种蜂窝增强泡沫塑料既可以作为低应变率场合的缓冲材料使用, 又可以应用于高应变率冲击下的抗爆场合。      

Peculiar mechanical properties of aluminium-magnesium,aluminium-copper and aluminium-zinc alloys at low temperatures

The paper reports on work hardening of solid solutions under tension at a constant rate of 7 × 10^?4s^?1, at temperatures of 1.6 to 300 K. The materials studied were single crystals of Al (0.62–9.0 at % Mg) and polycrystals of Al (0.62–10.4 at % Mg), Al (0.42 at % Zn) and Al (0.62 at % Zn). At very low temperatures, in addition to the softening due to maximum magnesium doping of aluminium, the authors found a softening associated with, first, an anomaly of the temperature dependence on the flow stress, second, an anomaly of the temperature dependence on the relative lengthening, and third, discontinuous flow.     

二维C/SiC复合材料准静态和动态拉伸力学性能

采用分离式Hopkinson拉杆装置和电子万能试验机研究了二维C/SiC复合材料在4种应变率（0.001、0.010、90.000和350.000 s-1）下的拉伸力学性能,计算并验证了动态试验中的应力平衡状态;采用SEM分析了复合材料在不同应变率下的破坏断口和失效机制;建立了复合材料包含损伤和应变率相关的本构方程。结果表明:二维C/SiC复合材料的应力-应变曲线都表现出非线性的特征。随着应变率的增加,二维C/SiC复合材料的拉伸强度从204 MPa增加到270 MPa,增加了33%,这表明复合材料的拉伸强度具有较强的应变率敏感性。复合材料在准静态和动态加载下表现出不同的破坏模式是由材料内部界面行为的应变率效应造成的。      

Microstructure and texture of copper/niobium composites processed by ECAE

The structure refinement is a challenge for conductors used for the winding of resistive coils producing non-destructive pulsed magnetic fields over 80T. These nanocomposite conductors composed of a conducting multiscale Cu matrix embedding Nb reinforcing nanofilaments are usually manufactured by using a Severe Plastic Deformation (SPD) process based on hot extrusion, accumulative cold drawing and bundling (ADB) steps [Thilly et al. Philos Mag A 82:925, 2002]. Equal-channel angular extrusion (ECAE) is investigated here as an alternative route since it may provide faster refinement to obtain the ultrafine structure needed for optimized electrical and mechanical properties of the conductors. Therefore, copper-niobium specimens obtained by hot extrusion were processed by ECAE at room temperature. The specific die of the ECAE tool used here is constituted by a round channel with three angles corresponding to a total equivalent strain of about 2.5. Deformed samples were examined by optical microscopy and characterized by hardness profiles and x-ray diffraction (texture pole figures). After one ECAE-pass, the shape of the samples is modified but no trace of damage appeared at the Cu-Nb interfaces. An increase of the hardness values localized in the copper matrix is revealed whereas the hardness of the niobium remains unchanged. Prior to ECAE, the hot extrusion process induced a fibre texture for both copper and niobium. Two fibre texture components were observed for copper: <111> and <200>. A single <110> fibre texture component is evidenced for the niobium. After ECAE a significant variation of the texture is observed in relation with the strong shear induced by this process.     

Densification behavior,mechanical properties and thermal shock resistance of tungsten alloys fabricated at low temperature

The low-temperature shrinkage of tungsten was greatly accelerated by the addition of trace Nb and Ni, and the addition of trace Nb and Ni also significantly promoted the final sintering density. The 99.1% of theory density for W–0.1 wt.%Nb–0.1 wt.%Ni material sintered at 1600 °C was obviously greater than 93.7% of theory density for W material sintered at 2000 °C. Ball milling treatment played an important role in promoting the sintering densification of W–0.1 wt.%Nb–0.1 wt.%Ni powder, and the powder milled for 10 h (W10) could be sintered to near full density (99.4% of theory density) at 1600 °C. The ball milling for 15 h has no effect in improving the sintering density, but it induced rapid growth of tungsten grains. The microhardness and tensile strength of the sintered tungsten alloys were highly dependent on its sintering density and grain size. Improving the sintering density while controlling the grain growth could effectively promote the microhardness and tensile strength. Furthermore, the improvement of thermal shock resistance of the W10 alloy was due to good microstructure and the increase in the tensile strength.     

Thermal properties of Zerodur at low temperatures

The linear thermal expansion of Zerodur has been measured from 20 to 300 K and the thermal conductivity from 2 to 100 K. For each property the temperature dependence appears to reflect the composite nature of the ceramic-glass.     

Thermophysical properties of epoxy compounds at low temperatures

Thermophysical properties of epoxy resin and its compounds are studied experimentally in the temperature range of 4.2–400 K. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 1, pp. 14–18, January–February, 1997.     

Transport properties of cold-worked aluminum at low temperatures

The electrical resistivity and thermoelectric power in annealed and cold-worked samples of Al and Al-Mg alloy have been measured between1.5 and8.5 K. The deviation from Matthiessen's rule is found to decrease with cold work, while the residual resistivity increases. The lattice imperfections also have strong effects on the thermoelectric power. A critical discussion focuses on the relation of and discrimination among these effects.     

Dielectric properties of glasses at ultra low temperatures

A temperature dependence in the dielectric constant of vitreous silica has been measured down to a few hundred microkelvin at frequencies between 110Hz and 10kHz. Homosil glass shows a logarithmic increase below 10 mK down to the lowest temperature of 0.61 mK. On the other hand, Suprasil glass exibits a saturation behavior following a logarithmic increase above 3 mK. These phenomena are discussed on the basis of the two level system.