Viscoelastic properties ofin situ lignin under water-saturated conditions

The viscoelastic properties of wood under water-saturated conditions have been studied in the temperature range 20 to 140° C at frequencies ranging between 0.05 and 20 Hz. It is demonstrated that the major transition in this temperature range is related to aglass transition, i.e. the glass transition of thein situ lignin. The difference in softening behaviour along and across the fibre direction is shown to be related to the stiffening effect of the cellulose microfibrils preferentially aligned along the fibre direction. The softening behaviour is also estimated for frequencies applicable to wood defibration processes, 10⁴Hz. The implications of the wood properties under these conditions are discussed.     

高强高导Cu-Fe合金的研究进展

综述了高强高导Cu-Fe合金的强化方法、制备、形变工艺及性能等的研究进展。结合形变及时效处理,提出了如何利用快速凝固中Cu-Fe合金的液相分离控制合金的凝固组织、合理开发三元及多元合金和采用电磁搅拌方法提高Cu-Fe合金的综合性能是未来研究的重要方向。     

基于铝热反应Cu-Fe二元合金的微观组织与摩擦性能研究EI北大核心CSCD

基于铝热法制备含2%(质量分数)Al的Cu-Fe合金,采用XRD,SEM,EDS和EBSD技术对Cu-Fe合金的相结构、微观组织进行表征,同时采用HVS-1000A维氏硬度仪和CFT-1材料表面性能测试仪测试Cu-Fe合金的硬度及抗磨损性能。结果表明:利用铝热反应可高效地制备Cu-Fe合金,成分可控,组织致密无夹杂,其中Fe相均匀地分布在Cu基体中,Cu和Fe的相界面结合良好;Fe相的硬度为322.2HV,基体Cu相的硬度为169.3HV,Cu-Fe合金的电导率为40.8 MS/m。铝热法制备的Cu-Fe合金具有较低的摩擦因数,平均摩擦因数为0.124,磨损率为2.17×10^(-3) mm 3·N^(-1)·m^(-1)。     

Creating textured substrate tapes of Cu-Fe alloys for second-generation high-temperature superconductors

It is established that Cu-1.6 at % Fe alloy tapes obtained through cold rolling to 98.9% followed by recrystallization annealing possess a sharp cube texture, which opens prospects of using thin tapes of this alloy as substrates for second-generation high-temperature superconductors. The optimum regime of annealing is determined that allows an alloy with sharp biaxial texture containing more than 97% cubic grains to be obtained. The yield stress of a 90-μm-thick Cu-1.6 at % Fe alloy tape upon recrystallization annealing at 800°C for 1 h amounts to 78 MPa, which is about three times higher than the value for a pure copper tape with sharp cube texture.     

Cu-Fe合金的强磁场固溶时效行为

将Cu-15%Fe(质量分数)合金在强磁场中进行不同同溶时效处理,研究了合金的时效行为.结果表明,施加10 T强磁场可以促进第二相Fe枝晶的球化,而且Fe枝晶的形貌受强磁场的球化作用与高温缓慢冷却引起的粗化作用的影响.在Cu-15%Fe合金1000℃同溶处理中,施加10 T强磁场使基体中的Fe含量降低了0.39%.这表明,强磁场在一定程度上促进了Fe在Cu基体中的析出,获得与缓冷相类似的效果;施加10 T强磁场固溶处理并在10 T强磁场作用下经500℃时效处理后,基体中的Fe含量较低.其原因是,施加强磁场后Fe原子的析出规律受温度制度和析出相磁性转变的共同影响.施加强磁场改变了原子的激活能,进而影响了原子的扩散行为.     

Anisotropy of elastic constants ofin situ Pb-Sn eutectic composite measured by pulse-echo method

Anisotropic elastic constants of Pb-Sn eutectic composites with layered structure have been measured by the pulse-echo method. The magnitude of the elastic constants was found to vary considerably depending upon the crystallographic directions as well as the directions relative to the plate-like eutectic constituents. The elastic constants of Pb-Sn eutectic bicrystal were determined taking thex1 andx3 axes, respectively, as the directions parallel to and normal to the growth direction of the eutectics. The interfacial energy of Pb-Sn layers was also determined. In addition, the anisotropy of the eutectics was confirmed by resistivity measurements.     

Microstructures and superconducting properties ofin situ V3Ga composite prepared by external diffusion process

A detailed study of the microstructures and superconducting properties of thein situ V₃Ga prepared by external gallium diffusion has been carried out. The structure of the final reacted layer has been found to be divided into two regions: an outer layer composed of multiple connected V₃Ga globules and an inner layer composed of filamentary V₃Ga surrounded by a Cu-Ga matrix. The particle-like V₃Ga in the outer region has a slightly higherT _c and, hence, higherH _c2 than the filamentary V₃Ga in the inner region. Therefore, it should be recognized that the measuredl _c is a combined contribution from both regions having a different magnetic field dependence ofJ _c.l _c at high magnetic field is primarily contributed by the outer region. Thel _c anisotropy of the tape conductor results from the anisotropic shape of filamentary V₃Ga in the inner region. The highest overallJ _c obtained is 2×10⁵ A cm^–2 at 12.5 T. Further optimization based on the microstructural control, which can be achieved by the appropriate design of the process, may yieldin situ V₃Ga composites having substantially improved properties.     

Thermal and electrical conductivity of binary magnesium alloys

Thermal conductivity is a key parameter for thermal design and management of the electronic components in their passive cooling processes. In this work, thermal and electrical conductivities of six groups of binary Mg alloys (Mg–Al, Mg–Zn, Mg–Sn, Mg–Zr, Mg–Mn, and Mg–Ca) in as-cast, as-solution, and annealed states were measured and the corresponding microstructures were observed. In both as-cast and as-solution states, thermal/electrical conductivities of the six groups of Mg alloys decreased with composition. Effects of solution treatment and annealing on thermal/electrical conductivities of the as-cast samples were also investigated and discussed. Moreover, the specific thermal/electrical resistivity (thermal/electrical resistivity increment of the alloy derived from one atom addition) of the solute elements for Mg alloys was drawn as follows, Zn < Al < Ca < Sn < Mn < Zr. Atomic volume difference of the solute elements with Mg atom (ΔV/V _Mg), valency, and configuration of extra-nuclear electron of the solute were believed as the main reasons for the differences.     

Thermal conductivity and mechanical properties of Sm-containing Mg-Zn-Zr alloys

This study investigated the effect of Sm additions on the microstructure, thermal conductivity, and mechanical properties of Mg-Zn-Zr alloy. The results indicate that the addition of Sm led to the formation of a rare-earth phase at the grain boundaries, and the grain size was significantly refined in the extruded state. The thermal conductivity of Mg alloy increased with the increase in Sm content because of the formation of a rare-earth phase that helps to dissolve the Zn atoms in the α-Mg matrix. Moreover, the as-extruded Mg alloy exhibited a higher thermal conductivity (up to124?W?(m?K)^?1) than its as-cast counterparts. The Sm-containing as-extruded Mg alloy showed excellent yield strength of up to 254?MPa, and also a good plastic deformation ability.     

Strength and ductility in ultrafine-grained wrought aluminum alloys

Strength and ductility are two of the most important mechanical properties of engineering materials. In this work, a 6061 aluminum alloy was subjected to multi-directional forging (MF) and aging treatment. The samples possess high strength and high ductility after processing. The strength of samples was enhanced by dispersing ultrafine precipitate particles within the grains, reducing grain-size and increasing dislocation density after MF and aging. The ductility was improved due to reducing the forging stress during aging. Moreover, a mass of dispersing ultrafine precipitate particles widespread within the grains after aging, which helps to accumulate dislocations, increase the dislocation storage capability and resist dislocation slip that lead up to increasing work hardening, the ductility was also enhanced. A linear strengthening elastic–plastic model was developed by simplifying the stress–strain curves. On this basis, the strength and ductility of ultrafine-grained (UFG) materials were discussed. This also provides fundamental insight into the mechanisms that govern the strength and ductility of UFG materials.     

Activation energy of conductivity in amorphous Bi-Se alloys

The dark conductivity activation energy of Se_100−xBi_x amorphous alloys (0 ⩽ x ⩽ 27) shows a drastic decrease for x ≈ 2. This result may be connected with the transition from p-type to n-type conduction.     

The possibility of reducing thermal conductivity in alloys

Reduction of thermal conductivity in nickel—titanium alloys by doping with elements having the greatest effect on phonon and electron components of thermal conductivity is considered.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 2, pp. 278–281, August, 1985.     

Low temperature thermal conductivity of twinned and untwinned indium-thallium alloys

The low-temperature lattice thermal conductivity of twinned and untwinned, martensitic and non-martensitic, indium-thallium alloys has been measured to probe the effect of twin boundaries on phonon thermal transport. The phonon scattering by electrons, sample surfaces, dislocations, and thallium impurities is accounted for adequately by existing theoretical models. The reduced lattice thermal conductivity seen in twinned samples is attributed to additional phonon scattering by twin boundaries and, for the polycrystalline samples, by grain boundaries. Phonon scattering by twin boundaries is much weaker than that generally reported for grain boundaries, and is well represented by an acoustic-mismatch model.