Production of tungsten-based composite materials from mechanically activated powders

The effects of the composition and metal additives on the compressibility of mechanically activated tungsten-based powder mixtures, the volume changes upon sintering, and the structure and strength of high-temperature composite materials are studied.     

钨基催化材料在直接醇类燃料电池中的应用研究

直接醇类燃料电池（DAFC）具有能量密度高、携带方便以及环境友好等优点。电极催化剂是改善DAFC性能的关键材料,目前DAFC催化剂要解决的关键问题是提高催化剂的电催化活性、抗CO等中间产物毒化能力以及降低催化剂成本,文中综述了2种钨基催化材料的制备、性能表征及其在DAFC中的应用研究进展,指出了目前钨基复合催化剂需要重点研究的基础问题。     

Deformation properties of sintered tungsten-based heavy alloys

The deformation properties of tungsten-based sintered alloys are studied. Plasticity diagrams are plotted for these alloys at deformation temperatures up to 900°C and various state-of-stress schemes. The properties of the tungsten-based sintered alloys are determined during alternating deformation. The joint action of the temperature (up to 900°C) and the state of stress on the ductility of the tungsten-based sintered alloys is analyzed. The results obtained are used to simulate damage accumulation for various methods of strain hardening of heavy alloys (rotational reduction, hydraulic forging, rolling in multiroll passes). Hydraulic forging is considered, and the limiting reductions are determined using the condition of impossible irreversible metal microfracture.     

Damping properties and impact strength of multilayer materials

Conclusions Crack blockage in the multilayer material investigated depends on the conditions of heat treatment of the dense material. The presence of porous metal layers in the multilayer material is responsible for a two- to threefold improvement in its damping properties.Translated from Poroshkovaya Metallurgiya, No. 12(216), pp. 29–31, December, 1980.     

纳米级(晶)钨基合金复合粉末的制备

综述纳米级(晶)钨基舍金复合粉末的制备技术,并对各种制备方法的原理、工艺、原料及所得产品进行分析和介绍,同时指出纳米材料的发展及应用前景。     

Plastic flow of a tungsten-based composite under quasi-static compression

A micromechanics study is carried out on the plastic flow of a tungsten “heavy alloy” under uniaxial compression. The alloy-composed of a continuous tungsten phase in a tungsten-nickel-iron “matrix”—is modeled as a dual-phase composite, with the tungsten phase approximated by aligned, uniformly distributed and equal-sized particles. The stress-strain behavior of each phase is assumed to be power-law hardening of the Ramberg-Osgood type. Stress-strain curves of the composite under uniaxial compression are computed numerically using several cell models representing different tungsten particle shapes. It is found that the overall stress-strain behavior of the composite is essentially independent of the particle shape. However, the character of the local plastic deformation changes dramatically with the inclusion geometry. Two simple formulae are given that approximate the overall flow behavior of the composite in terms of the tungsten volume fraction and the behavior of the individual phases.     

Crack propagation in ceramic materials under cyclic loading conditions

An analysis is presented which enables crack propagation rates under cyclic loading condiditions to be predicted from static slow crack growth parameters. A comparison of the predicted times to failure under cyclic conditions with available measured failure times, for several ceramic materials at ambient temperatures, suggests that there is no significant enhancement of the slow crack growth rate due to cycling. This is verified in a series of measurements of slow crack growth rates under static and cyclic conditions.     

循环荷载下岩石材料力学特性研究进展

工程实际中的岩体常常受到地质构造运动、工程施工及次生应力场等循环荷载作用,表现出与单调荷载不同的力学特性.为了更好地研究循环荷载作用下岩石材料的力学特性,对强度特征、变形特征及破坏特征3个方面进行了总结分析,同时对现有研究的局限性提出了几点建议:在更宽频率范围内研究频率对循环力学特性的影响,从而得出更为准确的结论;将现...     

Three-dimensional dynamic behaviour of the human knee joint under impact loading

Over the past 50 years, we have made remarkable advances in the use of bionic devices and solid organ transplants as replacement parts for failing tissues and organs. These approaches to tissue restoration, however, have a number of drawbacks. Thus, a new approach, regenerative biology and engineering, has been developed, consisting of the strategies of cell transplantation, bioartificial tissue constructs, and stimulation of regeneration in vivo. Cell transplants have been successfully used to restore articular cartilage and to treat Parkinson's disease in humans. In rats, transplanted fetal and embryonic stem cell line-derived cardiomyocytes have been shown to differentiate and integrate well with the ventricular myocardium, suggesting the feasibility of using such transplants to restore damaged cardiac muscle. Diabetic symptoms in humans have been alleviated by implanting a bioartificial pancreas consisting of islet cells microencapsulated in alginate. Hydroxyapatite matrixes can stimulate the regeneration of bone across large gaps. Collagenous artificial matrixes can stimulate the regeneration of dermis, and peripheral nerve grafts embedded in a fibrin clot containing fibroblast growth factor-1 stimulate some regeneration of spinal cord axons in adult rats. Future research in regenerative biology will focus on several issues: (1) providing adequate sources of cells for transplantation and bioartificial tissue construction and determining ways to prevent these cells from coming under attack by the immune system, (2) developing new and better materials to build better bionic devices and bioartificial constructs and to stimulate regeneration in vivo, (3) determining how many tissues of the body might contain reserve cells for regeneration in vivo, (4) analyzing the molecular differences between cells and environments of regenerating versus nonregenerating tissues, and (5) understanding the factors and mechanisms involved in the proliferation and patterning of regenerating tissues.     

冲击加载条件下金属粉末的动态力学性能分析

为研究金属粉末在冲击加载过程中, 粉末预压力对压坯动态力学响应的影响, 设计了基于分离式霍普金森压杆装置(split Hopkinson pressure bar, SHPB)的金属粉末高应变率冲击加载实验, 并结合一维应力波理论对预压后粉末压坯的力学性能进行分析。结果表明:在冲击过程中, 金属压坯会表现出较为明显的应变率效应; 加载率越大, 材料的应变能越大, 预压力越大, 应变硬化率越大; 在相同的加载条件下, 预压力越大, 压坯临界位移越小。     

钨纤维增强钨基合金挤压棒坯的脱脂工艺

在93W-Ni-Fe粉末中添加长2～3 mm的短钨纤维,用粉末挤压成形方法制备纤维定向排布强韧化的钨合金棒坯.对蜡基粘结剂挤压喂料进行DSC-TG热分析,采用扫描电镜、光学电镜对热脱脂后的挤压棒坯微观结构和表面形貌进行测试与表征,对比研究含纤维与不含纤维挤压棒坯的热脱脂行为.结果表明:1)挤压棒坯在热脱脂过程中极易产生...     

Liquid impact erosion mechanism and theoretical impact stress analysis in TiN-coated steam turbine blade materials

Coating of TiN film was done by reactive magnetron sputter ion plating to improve the liquid impact erosion resistance of steam turbine blade materials, 12Cr steel and Stellite 6B, for nuclear power plant application. TiN-coated blade materials were initially deformed with depressions due to plastic deformation of the ductile substrate. The increase in the curvature in the depressions induced stress concentration with increasing number of impacts, followed by circumferential fracture of the TiN coating due to the circular propagation of cracks. The liquid impact erosion resistance of the blade materials was greatly improved by TiN coating done with the optimum ion plating condition. Damage decreased with increasing TiN coating thickness. According to the theoretical analysis of stresses generated by liquid impact, TiN coating alleviated the impact stress of 12Cr steel and Stellite 6B due to stress attenuation and stress wave reactions such as reflection and transmission at the coating-substrate interface.