材料期刊网

LOW CYCLE FATIGUE AND CREEPFATIGUE BEHAVIOROF A HIGH TEMPERATURE ALLOY ON SMOOTH ANDNOTCHED SPECIMENS

Author H.J. Shi1) , S.L. Liu2) , Y.H. He1) and Z.X. Duan2) 1) Department of Engineering Mechanics , Tsinghua University , Beijing 100084 , China2) Laboratory of Material Mechanical Properties , Beijing Institute of Aeronautical Materials , Beijing 100095 , ChinaManuscript received 18 October 1998

金属学报(英文版)

A series of low cycle fatigue and creepfatigue tests on smooth specimens and notched specimens were performed with a high temperature alloy used in the manufacture of aeroengine turbine discs. The cyclic stressstrain behavior and fracture characteristics of the notched specimens were emphatically investigated. A comparison of fatigue behavior between smooth and notched specimens was done and lifetime of notched specimens was evaluated. At the same temperature, the fatiguecreep lives of the smooth specimens are far greater than that of the notched specimens.

关键词: low cycle fatigue , null , null , null

Microstructure and Mechanical Properties of ZrO_2-Ni Functionally Gradient Material

Jingchuan ZHU , Zhongda YIN and Zhonghong LAI(Dept. of Metals and Technology , Harbin Institute of Technology , Harbin , 150001. China)

材料科学技术（英文）

The fabrication. microstructure and mechanical properties of ZrO2-Ni functionally gradient materials (FGM ) have been studied. FGM as well as non-FG M of ZrO2-Ni system was developed by powder metallurgical process. X-ray diffractometer (XRD ). electron probe microanalyzer (EPMA), scanning electron microscope (SEM ) and optical microscope were employed to investigate the crystalline phases. chemical composition and microstructure Experimental results demonstrate that the composition and microstructure of ZrO2-Ni FGM have the expected gradient distribution. There are no distinct interfaces in the FGM due to the gradient change of components. that is, the constituents are continuous in microstructure everywhere. Moreover, Vickers hardness and flexural strength were measured for the common composites as a function of composition. It is made clear that the mechanical properties of the FGM vary corresponding to the constitutional changes as well

关键词:

Indirect Measurement of Material Thermal and Mechanical Properties during Welding

Dongqing LI , Jun TAO , Qingguo Meng , Hongyuan FANG

材料科学技术（英文）

By means of a newly developed non-contact detecting method, electronic speckle pattern interferometry (ESPI), a method of determining material property data during welding is studied. A TIG fixed-point welding process is modeled in which some achievements of simulation, such as the effect of welding pool on temperature field and nonlinear relation between convection coefficient and temperature, are all considered. In addition, by taking into account effect of heating rate, the workpiece is divided into near-weld zone and far-weld zone, which will be treated with different property values. When the displacement field computed with original property data is compared and matched with the experimental displacement field, which is measured by ESPI, these original data are adjusted properly. A group of raw properties are obtained and are corrected by statistical regression before they enter the simulation process again. By such a loop of “simulation-comparison-modification”, a set of property data that best satisfy the real condition are achieved finally. In such a way, a new method for measuring material properties during welding is found.

关键词: Material properties , null , null , null

Mechanical properties and damage tolerance of Y2SiO5

Journal of the European Ceramic Society

Y2SiO5 has potential applications as functional-structural ceramic and environmental/thermal barrier coating material. As an important grain-boundary phase in the sintered Si3N4, it also influences the mechanical and dielectric performances of the host material. In this paper, we present the mechanical properties of Y2SiO5 including elastic moduli, hardness, strength and fracture toughness, and try to understand the mechanical features from the viewpoint of crystal structure. Y2SiO5 has low shear modulus, low hardness, as well as high capacity for dispersing mechanical damage energy and for resisting crack penetration. Particularly, it can be machined by cemented carbides tools. The crystal structure characteristics of Y2SiO5 suggest the low-energy weakly bonded atomic planes crossed only by the easily breaking Y-O bonds as well as the rotatable rigid SiO4 tetrahedra are the origins of low shear deformation, good damage tolerance and good machinability of this material. TEM observations also demonstrate that the mechanical damage energy was dispersed in the form of the micro-cleavages, stacking faults and twins along these weakly bonded atomic planes. which allows the "microscale-plasticity" for Y2SiO5.

关键词: Y2SiO5;mechanical properties;damage;strength;fracture;yttrium silicate;ceramics;system;si3n4-sio2-y2o3;coatings;monazite;strength;phases

THE MECHANICAL BEHAVIOR OF LABORATORY CROSS-WELD SPECIMEN AND ITS RELATION WITH THE PRACTICAL CASES AT ELEVATED TEMPERATURE

Author S.T. TU , J.M. Gong and X. Ling Nanjing University of Chemical Technology , Nanjing 210009 , ChinaManuscript received 18 October 1998

金属学报(英文版)

In order to interpret the test results of crossweld specimens for application in practical welded components, the present paper studies the high temperature behavior of laboratory cross weld specimens in terms of the uniaxial material tests and numerical simulations. It is found that the crossweld specimen may be used for the high temperature strength assessment, but can hardly be used for life assessment of the practical welded components, which depends on the loading conditions of the components.

关键词: high temperature , null , null , null , null

Mechanical Properties of the TaSi₂ Fibers by Nanoindentation

Chunjuan Cui Jun Zhang Lin Liu Hengzhi Fu

材料科学技术（英文）

The Si-TaSi₂ eutectic in situ composite, which has highly-aligned and uniformly-distributed TaSi₂ fibers in the Si matrix, can be obtained when the solidification rate changes from 0.3 to 9.0 mm/min. It is very interesting that one or two TaSi₂ fibers are curved when the solidification rate reaches 6.0 mm/min, although it is very brittle in general. The formation mechanism of the curved fiber is discussed and mechanical properties of the TaSi₂ fibers are examined by nanoindentation. It is found that the hardness and the elastic modulus of the bended TaSi₂ fiber are much higher than that of the straight TaSi₂ fiber. Moreover, the reasons why the mechanical properties of the straight TaSi₂ fiber are different from that of the curved TaSi₂ fiber are discussed. This can be ascribed to internal stress which results from mismatch of the thermal expansion coefficients of the two phases and di®erent crystallographic orientations.

关键词: Si-TaSi₂ eutectic in situ composite , null , null , null

Investigation on the properties of Nb and Al doped Ti3SiC2 as a new interconnect material for IT-SOFC

International Journal of Hydrogen Energy

A modified layered ternary compound (Ti0.98Nb0.02)(3)(Si0.95Al0.05)C-2 was evaluated as a new interconnect material for intermediate temperature solid oxide fuel cells (IT-SOFC). The results indicated that the compound has low density (4.50 g/cm(3)), closer matched thermal expansion coefficient with Y2O3 stabled ZrO2 (9.0 x 10(-6)/K), low room temperature electrical resistivity (24 mu Omega cm), and good mechanical properties and machinability. During the isothermal oxidation at 600 degrees C-800 degrees C, a monolithic layer with the mixture of rutile TiO2 and amorphous SiO2 formed on (Ti0.98Nb0.02)(3)(Si0.95Al0.05)C-2. Its oxidation kinetics roughly follows a parabolic law, the rate constant is 0.45, 1.26, 1.57 x 10(-7) mg(2)/cm(4) s at 600 degrees C, 700 degrees C, 800 degrees C, respectively. After the oxidation at 700 degrees C and 800 degrees C in air for 100 h, its area special resistance is 5 and 12 m Omega cm(2) at the corresponding oxidation temperature, respectively. In oxidizing environment, (Ti0.98Nb0.02)(3)(Si(0.95)A(10.05))C-2 is very stable, and has not Cr or other element volatilization. All above determined properties of (Ti0.98Nb0.02)3 (Si0.95Al0.05)C-2 are favorable for its application as interconnect in IT-SOFC. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

关键词: MAX phase;Interconnect;SOFC;Oxidation;Area specific resistance;oxide fuel-cells;alloy interconnects;air

Microstructure Characterization and Mechanical Properties of FGH 95 Turbine Blade Retainers

TAO Yu , JIA Jian , LIU Jiantao

钢铁研究学报(英文版)

FGH 95 is a powder metallurgy (P/M) processed superalloy, which was developed in the 1980s in China. One of the applications of FGH 95 was for high pressure turbine blade retainers. The manufacturing processes used to produce FGH 95 blade retainers consisted of atomization by plasma rotating electrode process (PREP), hot isostatic pressing (HIP) at super-solvus temperature and a heat treatment with sub-solvus solution. The material had an equiaxed grain structure (ASTM 6.5-7.5). The γ' precipitates in As-HIP FGH 95 showed a tri-model distribution. Carbides in the alloy were type of MC and precipitated at grain boundaries. The prior particle boundaries (PPB) in the material were found to originated mainly from γ' phase. Statistics of the mechanical properties data from batch production of the FGH 95 blade retainers were investigated. The As-HIP FGH 95 blade retainers showed high strength at room temperature and 650℃, excellent creep resistance and outstanding stress rupture strength at 650℃.

关键词: FGH95;As-HIP;P/M superalloy;blade retainer;microstructure;mechanical property

THE EFFECT OF SUBZERO TREATMENT ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Y_2O_3-ZrO_2 CERAMIC

LI Ying , WANG Xiaotian , JIN Zhihao Xi'an Jiaotong University , Xi'an , China SHl Guoshun Beijing Measuring and Analysing Center.Beijing , China

金属学报(英文版)

The effect of subzero treatment on the microstructure and mechanical properites of Y_2O_3- ZrO_2 ceramic have been investigated by TEM,X-ray diffraction and test of mechanical properties.It was shown that the microstructre of 3Y-PSZ after subzero treatment by liquid nitrogen exhibits very long and parallel laths of m-phase and some microcracks around the larger and finer lath of m-phase may be discovered.Suitable subzero treatment can improve the strength and toughness of Y-PSZ efficiently because of decreasing the stability of t-phase and incresing the amount of t-m transformation when exerting a stress.However,when the time of subzero treatment exceeds,the over aging effect may arise.which can decrease the strength and toughness of the material.

关键词: Y_2O_3-ZrO_2 partially stabilized zirconia(PSZ) , null , null

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF IN-SITU FORMATION FIBROUS POLYTYPE AlN COMPOSITE-MATERIAL

LI Zonghuai CHEN Shengqi ZHOU Yanchun XIA Fei Institute of Metal Research , Academia Sinica , Shenyang , China Professor , Institute of Metal Research , Academia Sinica , Shenyang 110015 , China

金属学报(英文版)

In-situ formation fibrous polytype AlN composite ceramic materials was prepared from AlN-Y_2O_3-SiO_2 system.In comparison with AlN ceramics,both bending strength and fracture toughness of the composite materials are much bettered.Microstructural observation revealed that a lot of epitaxial growth fibrous AlN polytype occurred in matrix.Y_2O_3 seems to act as a densifier for in-situ formation materials and as medium for growth of fibrous polytype.SiO_2 is the growth promoter for fibrous polytype.The occurrnce of fibrous polytype may increase the strength and toughness of AlN ceramic composite mateirals.

关键词: AIN ceramics , null , null