Electrical resistivity of the composites based on the iron disilicide-molybdenum trioxide-glass system

Translated from Poroshkovaya Metallurgiya, No. 9(345), pp. 43–47, September, 1991.     

Influence of porosity and hBN content on the damping capacity of metal matrix composites

ABSTRACT

Sintered iron samples were produced using different pressing loads, resulting in different residual porosities of approximately 14%, 18%, 22% and 30%. Iron-matrix composites, containing 2.5, 5.0, 7.5 and 10.0 %vol. of dispersed hexagonal boron nitride (hBN) particles, were also produced. The influence of these parameters on the amplitude-dependent damping capacity was assessed using a dynamic-mechanical analyser. The simultaneous effect on mechanical strength was assessed through a tensile test. The microstructure was analysed with optical and electronic microscopy and quantitatively evaluated through a digital image analysis. It was verified that the increase of porosity did not lead to a representative increase in the damping capacity of sintered iron. On the other hand, higher hBN content leads to a higher damping capacity due to the introduction of robust new damping mechanisms. However, hBN reservoirs, which are bigger and more elongated than the pores, are more detrimental to mechanical strength.     

Metal-ceramic cohesion and the image interaction

A detailed understanding at the microscopic level of the strength of bonding at metal-ceramic interfaces, including its dependence on the crystallographic structure and chemical nature of the components, requires a model of the interatomic forces. Interatomic force models and computer simulation are widely used in the study of metal-metal and ceramic-ceramic boundaries but have not yet been applied to metal-ceramic. Recently however improvements in the microscopic modelling of metallic and ceramic cohesion together with the development of more powerful computers have opened possible ways of simulating the metal-ceramic interface which we are currently investigating. A particularly important component of the adhesive interaction across a metal-ceramic interface is believed to be the electrostatic image interaction which has no place in simple models of adhesion based on chemical bonding. This paradoxical situation is resolved. The image interaction is really a classical concept in the continuum electrostatics of point charges near a conducting surface, and makes no reference to discrete atoms. Nevertheless its equivalent attractive force close to a real metal surface can be calculated quantum mechanically for simple geometries. Fortunately, the results of these quantum mechanical calculations can be simulated by a classical interatomic force model, suggesting a way forward for atomistic simulation.     

Effect of porosity content on composition of W/ZrC composites produced by displacive compensation of porosity (DCP) method

Abstract

Tungsten based composites such as W/Cu have successfully been used in high temperature environments. In order to reduce the weight and improve their erosion resistance, W/ZrC composite has already been developed via displacive compensation of porosity method by Dickerson et al. The aim of this work was to investigate the effect of preform porosity on the composition of final composite. For this purpose, a mixture of tungsten carbide powder and PVA was cold isostatic pressed to make a porous tungsten carbide preform. The porous perform was debinded for 14·4×10³ s at 673 K and sintered for 14·4×10³ s at 1673 K. The sintered perform was then infiltrated by molten Zr₂Cu at 1573 K for 25·2×10³ s. The cross-section of infiltrated specimens was studied using scanning electron microscopy equipped with an energy dispersive spectroscope analyser as well as X-ray diffraction. The results indicated that the amount of tungsten and zirconium carbide phases in final composite increased as the porosity of WC preform increased. The relative density of W/ZrC composite reduced with increasing initial porosity of sintered preform.     

Studies on synthesis and microstructure evolution of multiphase in-situ composites based on Mo-Cr-Si system

This paper presents the results on in-situ synthesis of refractory metal-intermetallic composites (RMICs), Mo-16Cr-4Si and Mo-11Cr-9Si (wt.%) multiphase alloys and their characterization. The alloys were prepared from the oxides of molybdenum and chromium by their coreduction with Si as reductant. Exothermic nature of the synthesis reactions resulted in the formation of consolidated composite as a product in a single step. As-reduced alloys were remelted by arc melting and heat treatment was given. The evolution of phases and the microstructure were studied by XRD, SEM, and EDS analysis. The multiphase microstructure consist of the silicide phases (Mo,Cr)₃Si + (Mo,Cr)₅Si₃ for hypereutectic and (Mo,Cr)₃Si phase distributed in bcc matrix comprising essentially a solid solution of (Mo,Cr) for hypo-peritectic composition. Comparative studies of the synthesized alloys were also carried out to the composition, phases, microstructure, hardness and their oxidation behavior.     

基于均匀化理论的复合材料安定性分析方法

周期性非均质复合材料具有微观结构特征,需要均匀化理论进行宏观和微观的多尺度分析来研究其性能表现。针对其耐久强度性能,应用塑性极限安定下限定理,特别分析了其在长期交变载荷下的安定状态。结合工程应用目标,提出一种全新的代表性单元边界条件,结合圆锥二次优化算法进行数值计算,可以从材料微结构和组分性能出发,经过弹性应力场求解确定位移边界载荷数值,最终由优化求解得到复合材料板材的面内塑性性能容许域。所求得的应力域以单向应力为基,可根据结构宏观的单向应力状态变化幅值直接进行安定状态与否的判定。通过文中的多个算例,验证了所编写的软件及计算流程的可行性及数值准确性,展示了该方法在工程模型中的应用场合和工程实践意义。      

基于均匀化理论的复合材料安定性分析方法

周期性非均质复合材料具有微观结构特征,需要均匀化理论进行宏观和微观的多尺度分析来研究其性能表现.针对其耐久强度性能,应用塑性极限安定下限定理,特别分析了其在长期交变载荷下的安定状态.结合工程应用目标,提出一种全新的代表性单元边界条件,结合圆锥二次优化算法进行数值计算,可以从材料微结构和组分性能出发,经过弹性应力场求解确定位移边界载荷数值,最终由优化求解得到复合材料板材的面内塑性性能容许域.所求得的应力域以单向应力为基,可根据结构宏观的单向应力状态变化幅值直接进行安定状态与否的判定.通过文中的多个算例,验证了所编写的软件及计算流程的可行性及数值准确性,展示了该方法在工程模型中的应用场合和工程实践意义.     

Assessment of porosity and structure of powder materials based on mechanically activated Ni-Fe-NaCl charges

Electron-probe microanalysis methods were used to study the formation of structure and the distribution of various components in high-porosity powder materials during heat treatment of compacts based on Ni-Fe-NaCl charges mechanically activated in fluid media. We confirmed the hypothesis that agglomerates are formed during mechanical activation of Ni-and Fe-based composite-particle charges in fluid media. A causal relationship was established between formation of structure in compacts and structure of the high-porosity powder material after heat treatment. A technique was proposed for determining the local porosity of the sintered high-porosity powder material. The structure of the high-porosity powder material was found to consist of large pores surrounded by powder material containing pores of smaller diameter.     

Biodegradation of the composites based on polyethylene and sevilene with natural rubber

The mechanical properties, the water absorption, and the resistance to soil microrbiota of the composite films based on polyethylene and ethylene-vinyl acetate copolymers with additives of natural rubber are studied. The intensity of the biodegradation of the composites is shown to depend on both the mixture composition and the content of vinyl acetate units in a copolymer.