(SiCp+C)/MoSi2复合材料的组织结构及力学性能

通过热压烧结工艺制得了(SiCp+C)/MoSi2复合材料,测试分析了材料的组织结构、室温和高温力学性能.结果表明:(SiCp+C)/MoSi2复合材料主要由MoSi2(大量),α-SiCp(大量),Mo5 Si3(多量)和β-SiC(少量)组成,密度为5.12g/cm3,相对密度为91%;增强相的粒径＜30μm,体积分数为39%.其室温硬度、抗弯强度和断裂韧性分别为12.2 GPa,530MPa和7.2MPa·m1/2;材料在800℃的维氏硬度为8.0 GPa,1 200和1400℃的抗压强度分别为560MPa和160MPa.与非增强MoSi2相比,材料的各种力学性能都有大幅度的提高.     

Interfacial reactions in Al-Mg (5083)/AI2O3p composites during fabrication and remelting

The interface reactions between a-Al₂O₃ particles and 5083 Al-Mg alloys during fabrication by compocasting and subsequent remelting at 800 °C for 30 minutes have been studied using analytical transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Experimental results show that MgO is the main reaction compound produced by the reaction 3Mg (1) + A1₂O₃ (s) = 3MgO (s) + 2A1 (1). The MgO crystals formed by interfacial reaction are very small (about 5 to 20 run in diameter), and the reaction zone is about 50 to 80-nm wide for as-cast materials and about 100 to 150 nm after remelting. The reaction kinetics is controlled by seepage of Mg and release of Al (1) along the newly formed MgAl₂O₄ or MgO grain boundaries. Because of the large volume expansion during the formation of MgO from the reaction between Mg (1) and A1₂O₃ and because of the low diffusivity in MgO crystals, the reaction rate is very low.     

Microstructure of the Ti3Al(Nb)/TiB composite produced by combustion synthesis

The combustion synthesis technique was used to produce the intermetallic composite α₂-Ti₃Al(Nb) reinforced with TiB fibers. The microstructure was examined by scanning electron microscopy (SEM), X-ray diffraction analysis, and transmission electron microscopy (TEM). Neither the β nor the β₀ phase was found in the intermetallic matrix. The TiB phase with B27 structure existed in the form of polycrystalline faceted whiskers growing in the (010) direction of the unit cell. No defined crystallographic relationship between the TiB whiskers and the matrix was found in this investigation. W.Y. YANG, Postdoctoral Fellow, on leave from the University of Science and Technology Beijing, Beijing, People’s Republic of China     

Combustion in Layered Ni + Al and Ti + Al + C Powdered Mixtures

Russian Journal of Non-Ferrous Metals - This study is devoted to the technology of producing cermet coatings using self-propagating high-temperature synthesis (SHS). The importance of the study is...     

Interfacial Microstructure in a B4C/Al Composite Fabricated by Pressureless Infiltration

In this work, B₄C particulate-reinforced Al composite was fabricated by a pressureless infiltration technique, and its interfacial microstructure was studied in detail by X-ray diffraction as well as by scanning and transmission electron microscopy. The B₄C phase was unstable in Al melt during the infiltration process, forming AlB₁₀-type AlB₂₄C₄ or Al_2.1B₅₁C₈ as a major reactant phase. The Al matrix was large grains (over 10 μm), which had no definite orientation relationships (ORs) with the randomly orientated B₄C or its reactant particles, except for possible nucleation sites with { 011}_{\textB4 \textC} \{ 011\}_{{{\text{B}}_{4} {\text{C}}}} almost parallel to {111}_Al at a deviation angle of 1.5 deg. Both B₄C–Al and reactant–Al interfaces are semicoherent and free of other phases. A comparison was made with the SiC/Al composite fabricated similarly by the pressureless infiltration. It was suggested that the lack of ORs between the Al matrix and reinforced particles, except for possible nucleation sites, is the common feature of the composites prepared by the infiltration method.     

Interfacial phenomena in some slag-metal reactions

In the present work, the change of the interfacial tension at the slag-metal interface for sulfur transfer between molten iron, slag, and gas phases was monitored by X-ray sessile drop method in dynamic mode in the temperature range of 1830 to 1891 K. The experiments were carried out with pure iron samples immersed partly or fully in the slag phase. The slag consisted of 30 wt pct CaO, 50 wt pct Al₂O₃, and 20 wt pct SiO₂ (alumina saturated at the experimental temperatures) with additions of FeO. Metal and slag samples contained in alumina crucibles were exposed to a CO-CO₂-SO₂-Ar gas mixture with defined oxygen and sulfur partial pressures, and the change of the shape of the metal drop was determined as a function of time. The equipment and the technique were calibrated by measurements of the surface tensions of the pure Cu, Ni, and Fe containing two different amounts of dissolved oxygen. A theoretical model was developed to determine the sulfur content of the metal as a function of time on the basis of sulfur diffusion in the slag and metal phases as well as surface tension-induced flow on the metal drop surface. Attempts were made to compute the interfacial tensions on the basis of force balance. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS.     

Interfacial Reactions in Al-Mg (5083)/SiCp Composites during Fabrication and Remelting

The interfaces of aluminum alloy composites (5083) reinforced by SiC particles (as-received, oxidized 3.04 wt pct and 14.06 wt pct) were studied. The composites were fabricated by compocasting and certain samples were also remelted at 800 °C for 30 minutes. The reaction mechanisms between SiC _p and liquid Al and between the SiO₂ layer and Al(Mg) are discussed. The crystal boundaries of the MgO (or MgAl₂O₄) reaction products are believed to be the diffusion paths (or channels) during the interfacial reactions. A SiO₂ layer, formed by oxidation of the SiC particles prior to their incorporation into the melt, plays an important role in preventing the SiC _p from being attacked by the matrix. The interfacial reaction products are affected by both the alloy composition and the thickness of the initial SiO₂ layer.     

Interfacial properties of self-reinforced composite poly(methyl methacrylate)

The authors describe ten years of experience in breast reconstruction in the Department of Plastic and Reconstructive Surgery in the District Hospital of Santarém--Portugal. Ninety-nine patients were treated with 106 reconstructions, most of these were immediate and some were delayed. The authors were interested in providing an adequate volume, but also into obtaining an acceptable aesthetic result. This contributes considerably to the psychological recovery of the patients.     

On the reactions 2 C + O2 and C + CO2 at very low pressure

In an ultra high vacuum heterogeneous gas reactions such as 2 C + O₂^G → 2 CO^G and C + CO₂^G → 2 CO^G often show a less complicated reaction path than under normal pressure. In the present study the graphite sample is a commercial light‐bulb filament, which is extremely resistant against oxidation. Under low pressure the combustion reaction is of first order with a continuous transition to zero order at temperatures between 900 and 1300 K depending on the oxygen pressure. The Boudouard reaction behaves similarly but obeys zero order only around 2000 K and for CO₂ pressures around 1 bar. The measured and the statistically calculated reaction rates agree well. An insight of the details of the reaction and chemisorption is determined by the evaluation of experiments carried out in an ultra high vacuum using isotopes such as ¹³CO₂^G. The Boudouard equilibrium for graphite can be reached only catalytically, e.g., with sponge iron in statu nascendi.     

TC4合金基体上激光熔敷钛、铝、二氧化硅碳粉末的显微组织

Laser cladding experiment of Ti + Al + SiO2 + C was carried out on Ti6Al4V alloy substrate, thenthe microstructure of the clad layer was analyzed with SEM and its Anti - oxidation function was discussed.Analyses microstructure show that the clad coating can be divided into three zones along the depth direction:clad, binding and heat - affected zones. Ti5Si3 in the clad zone exists in the form of fine dendrites, TiAl matrix filling among Ti5Si3 dendrites plays a role of connecting the Ti5Si3 with the TiAl3 and transferring load,so the clad coating has been strengthened obviously.     

Microstructure of laser clad Ti ＋ Al ＋ SiO2 ＋ C powders on Ti6Al4V alloy

Laser cladding experiment of Ti ＋ Al ＋ SiO2 ＋ C was carried out on Ti6Al4V alloy substrate, then the micmstructure of the clad layer was analyzed with SEM and its Anti - oxidation function was discussed. Analyses microstructure show that the clad coating can be divided into three zones along the depth direction： clad, binding and heat -affected zones. Ti5Si3 in the clad zone exists in the form of fine dendrites, TiAI matrix filling among Ti5Si3 dendrites plays a role of connecting the Ti5Si3 with the TiAl3 and transferring load, so the clad coating has been strengthened obviously.     

模具用Ti(C,N)/Al2O3陶瓷材料的微观结构与力学性能

新型模具材料的开发是当前模具研究领域的重要内容之一.采用热压工艺制备了一种模具用Ti(C,N)/Al2O3复相陶瓷材料,并研究了该材料的制备工艺、微观结构和力学性能.研究表明以稀土氧化物为添加剂,Ti(C,N)/Al2O3陶瓷材料具有良好的微观结构和力学性能.抗弯强度、断裂韧度和硬度分别达到980 Mpa、6.0 Mpa·m1/2和19.2 Gpa,分别比纯Al2O3陶瓷材料提高96%、57%和5%.材料的增韧机理主要是裂纹桥联、裂纹偏转、裂纹分支以及部分纳米Ti(C,N)晶粒的晶内断裂机制.     

Reaction zone microstructure in a Ti3Al + Nb/SiC composite

A composite of Ti-25Al-13Nb (atomic percent) matrix with a continuous SiC fiber (SCS-6) reinforcement was fabricated by hot pressing powder cloths and mats of fiber. The fiber/matrix reaction zone was studied using scanning electron microscopy (SEM) and transmission electron microscopy/analytical electron microscopy (TEM/AEM) techniques. The extent of reaction was determined, phases were identified, and solute partitioning among the phases was determined. It was found that the matrix had reacted only with a portion of the carbon-rich outer layer of the SCS-6 fiber. The reaction zone contained two concentric zones which are distinguished by the presence of different carbide phases. Both zones contained a hexagonal Si-bearing phase, and one of the zones also contained some fine scattered porosity. The results are discussed with reference to available phase equilibria data. This paper is based on a presentation made in the symposium “Interfaces and Surfaces of Titanium Materials” presented at the 1988 TMS/AIME fall meeting in Chicago, IL, September 25–29, 1988, under the auspices of the TMS Titanium Committee.     

Interfacial fatigue in a fiber reinforced metal matrix composite

An experimental investigation of interface fatigue in a fiber reinforced metal matrix composite has been conducted. For this purpose, the cyclic traction law (the relationship between the fiber stress and the pullout displacement) was measured using fiber pullout tests. On the first loading cycle, the traction law was found to be parabolic, in accord with predictions of a micromechanical model based on a constant interface sliding stress. Upon subsequent unloading and re-loading, the relationship changed, following trends which suggest that the sliding resistance degrades with cyclic sliding. Such effects have been confirmed through SEM examinations of the fiber coatings following fatigue testing. Furthermore, the degradation was found to be greatest near the plane of the matrix crack. The results are consistent with the notion that the degradation in sliding stress occurs most rapidly in regions where the relative sliding distance (fiber/matrix) is greatest. A phenomenological model incorporating such degradation is presented and compared with the experimental measurements.