关键词： 热压烧结   铜基   氧化铝   复合材料   显微结构  

摘要： 采用热压烧结法制取了超细Ａｌ２Ｏ３Ｐ／Ｃｕ复合材料，对其烧结态、轧制态、退火态的显微组织、拉伸断口及界面进行了观察与分析。结果表明，增强颗粒在基体中分布均匀，细化了晶粒，轧制后组织进一步致密、细化，该材料具有良好的热稳定性；拉伸断口为韧窝和准解理混合断裂。能谱分析说明，界面上存在元素的扩散；热力学分析表明，界面上有化学结合，界面结合状态良好。

关键词： Materials science  

摘要： The basic objective of Q-mode factor analysis, a multivariate statistical technique based on the interrelation between samples, is classification of a suite of samples characterized by a large number of variables. The technique has been applied in modeling the microstructural heterogeneity present in a naturally occurring complex material. Significance of results is discussed with regard to the classification of multicomponent multiphase materials in general. (C) Elsevier Science Inc., 1998.

关键词： IASCC   microstructure   irradiation   austenitic stainless steel   RIS   CERT  

摘要： Microstructural evolution of proton-irradiated austenitic stainless steels and Inconel 600 alloy were studied in the temperature range interesting to light water reactor (LWR) core conditions. Radiation-induced solute segregation was observed in all irradiation temperatures at dose of 0.1 dpa and above. Constant extension rate test (CERT) was performed to study the irradiation-assisted stress corrosion cracking (IASCC) behavior of these alloys. Void swelling, dislocation and loop structures, and phase transformation were studied to understand the relationship of microstructural evolution to the IASCC phenomenon. It is found that in low carbon austenitic stainless steels, the gamma --> alpha phase transformation could play an important role in stress corrosion cracking mechanism. Twining dislocations were observed in 304L specimens irradiated at 230 degreesC to 1 dpa.

关键词： acoustic   microstructures   anisotropic materials   constitutive behaviour   nondestructive evaluation  

摘要： In general, finite plastic deformation is accompanied by microstructural material property changes such as texture change and growth of localized slip bands. However, it is very difficult to evaluate these microstructural material property changes nondestructively by means of the usual methods used to date. The ultrasonic nondestructive evaluation method proposed by the author has been successfully applied to the evaluation of plastically deformed state. The purpose of the present paper is to formulate precisely a generalized acoustoelastic theory for plastically deformed solids with finite plastic deformation and, moreover, to provide a method of nondestructive evaluation of the plastically deformed state, i.e, yield surface, texture change and the occurrence of the instability associated with the microslip band. (C) 1998 Elsevier Science Ltd. All rights reserved.

关键词： Ceramic materials  

摘要： The transformation toughening mechanism in zirconia-toughened ceramics is temperature limited. An attempt has been made to design a ternary partially stabilised zirconia alloy, based on CeO2-MgO-ZrO2, in which the transformation toughening component cf the measured mechanical properties is retained at low to intermediate temperatures, while other mechanisms for improving strength and toughness are invoked and become dominant at high temperatures. Mechanical property results indicate that the microstructures developed, which contain elongated, dispersed tetragonal zirconia particles, may produce useful toughening enhancement. However, the material fabrication route used requires refinement. (C) 1997 Elsevier Science Limited and Techna S.r.l.

摘要： The processing response of a 70% Si3N4 – 30% barium aluminum silicate (BAS) ceramic matrix composite was studied by pressureless sintering, at temperatures ranging from 1740°C, which is below the melting point of BAS, through 1950°C. The relationship between the processing parameters and the microstructural constituents, such as morphology and amount of β-Si3N4 whisker, and crystallization of the BAS matrix, was evaluated. The mechanical response of this array of microstructures was characterized for flexural strength, at test temperatures through 1300°C, as well as fracture behavior. The indentation method was employed to estimate the fracture resistance at room temperature. The composite that was sintered at 1920°C for 120 minutes with a fine microstructure consisting of β-Si3N4 whiskers about several microns in length had the flexural strength and critical fracture toughness averaging about 963 MPa and 5.5 MPa√m, respectively. The BAS glass ceramic was found as an effective liquid phase sintering aid to attain full densification and complete α to β-Si3Nu phase transformation in this material. The BAS matrix can be crystallized almost completely, which significantly benefits the high temperature strength of this composite. At 1300°C, the composite can hold a flexural strength of about 500 MPa. The improvement of fracture toughness was achieved by introducing some abnormally grown whiskers into the composites. The microstructure of the material appears to be more sensitive to the characteristics of Si3N 4 starting powders. It was found that the addition of coarse silicon nitride powder encourages the abnormal growth of β whiskers. These large whiskers have considerable contributions to the toughening of materials. Subsequently, the influence of sintering time on grain growth was considered for the various Si3N4 starting powder size distributions. In particular, the β-Si3N4 particles in starting powders are modeled as nuclei for the final microstructure.

摘要： Metal-matrix composites (MMCs) have potential as load bearing components for particular functional requirements. However, MMCs are more difficult to form than conventional metals and alloys due to the tendency of suffering microstructural damage at low plastic strains. It is thus of importance to understand the forms of microstructural damage, its level and spatial distribution. In this work, three main areas of investigation related to damage accumulation in MMCs were considered: the hydrostatic extrusion of MMCs, a theoretical investigation of scale effects in MMCs and plane strain compression experiments on model composites to study load transfer and fibre distribution effects on the patterns of plastic flow in the matrix. In the experiments on the hydrostatic extrusion of particulate MMCs, it was found that damage occurred in the form of reinforcement cracking, that the amount of damage varied linearly with applied plastic strain and that the rate of damage accumulation depended on the morphology of the reinforcement. The extrusion process was examined in regard to its ability to limit or suppress damage through the action of high compressive hydrostatic pressures. A slip-line field analysis was adopted to relate the effect of process parameters such as the amount of reduction and die angle to the magnitude and distribution of hydrostatic pressure in the extrusion dies. The linear relationship between damage and applied plastic strain was explained using a micro-mechanical description of the response of MMCs to plastic flow and the effect of microstructural variables such as volume fraction, shape and size of the reinforcement on the rate of damage accumulation was discussed. In addition, the tensile properties of MMCs subsequent to hydrostatic extrusion were quantified and the effect of previous extrusion was described in terms of the strain hardening of the matrix materials and the damage accumulation in the reinforcement materials and their influence on the s

关键词： 水泥基   宏观缺陷  

关键词： 强韧化   材料   损伤力学   微结构  

摘要： 典型材料与微结构的强韧化力学原理（１９９４—１９９６年工作总结）国家自然科学基金重大项目“材料损伤、断裂机理和宏微观力学理论”子课题国家自然科学基金会和国家科委攀登项目共同资助的重大项目“材料损伤、断裂机理与宏微观力学理论”的０５课题“典型材料与微结...

关键词： 纳米硅薄膜   电导率   光学带隙  

摘要： 用退火的方法改变了纳米桂（nc－Si：H）薄膜的微结构。用Raman散射和共振核反应方法分析了薄膜的微结构变化。结果表明，薄膜的氢含量是影响薄膜光学带隙的主要因素，而薄膜的晶态体积比和晶粒尺寸是影响薄膜电导率的主要因素。