材料期刊网

TEM STUDY OF TWINNING ORIENTATION RELATIOSHIP BETWEEN A AND B MARTENSITE VARIANTS IN A CuZnAl SHAPE MEMORY ALLOY

SHEN Guangjun WANG shidong ZHANG Jinping Lab.of Solid State Microstructure , Nanjing University , Analysis and Testing Centre , Southeast University , Nanjing , China Associate Professor , Analysis and Testing Centre , Southeast University , Nanjing , 210018 , China

金属学报(英文版)

A secondary twinning orientation relationship between A and B martensite variants in a CuZnAl shape memory alloy was confirmed under TEM observation.The twin plane, (50),is a linear combination of (8)and(1 0 10)planes,which are twin planes of A:C and A:D type pair respectively.

关键词: shape memory alloy , null , null , null

Failure analysis of corrosion cracking and simulated testing for a fluid catalytic cracking unit

Journal of University of Science and Technology Beijing

The failure of a fluid catalysis and cracking unit (FCCU) in a Chinese refinery was investigated by using nondestructive detection methods, fracture surface examination, hardness measurement, chemical composition and corrosion products analysis. The results showed that the failure was caused by the dew point nitrate stress corrosion cracking. For a long operation period, the wall temperature of the regenerator in the FCCU was below the fume dew point. As a result, an acid fume NOx-SOx-H2O medium presented on the surface, resulting in stress corrosion cracking of the component with high residual stress. In order to confirm the relative conclusion, simulated testing was conducted in laboratory, and the results showed similar cracking characteristics. Finally, some suggestions have been made to prevent the stress corrosion cracking of an FCCU from re-occurring in the future.

关键词: stress corrosion cracking;fluid catalytic cracking unit;dew point;failure

A CHALLENGE FOR BIAXIAL AND TRIAXIAL CREEP TESTING

M. Sakane (Department of Mechanical Engineering , Faculty of Science and Engineering , Ritsumeikan University , 1-1-1Nojihigashi Kusatsu-shi Shiga , 525-8577 , Japan)S. Mukai (Power Reactor and Nuclear Fuel Development Corporation , 4002 Narita-cho Oarai-cho Ibaragibun Ibaragi , 311-13 , Japan)

金属学报(英文版)

This paper describes new methods for biaxial and triaxial creep testing. Biaxial tension and triaxial tension creep testers were developed. The performance of the machines was described and some test results were discussed. Stress biaxiality had almost no effect on the creep deformation and Mises potential was suitable for describing the creep deformation under biaxial and triaxial stress states. Stress biaxiality had a small influence on prolonging creep rupture time under the constant Mises stress condition.A new triaxial tension creep testing method was discussed together with the shape of the triaxial creep specimen.

关键词: creep , null , null , null , null

Microsample tensile testing of nanocrystalline copper

Scripta Materialia

The tensile properties of nanocrystalline copper with grain sizes <100 nm produced by surface mechanical attrition treatment have been characterized using a microsample testing technique. The nanocrystalline copper exhibits a yield strength as high as 760 MPa, with a small elongation to failure. Factors leading to the high strength and low ductility are discussed. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

关键词: nanocrystalline materials;strength;ductility;fracture;copper;mechanical-behavior;metals;microstructure;ductility;strength;fatigue;alloy;cu

Evaluation of Young's Modulus and Residual Stress of NiFe Film by Microbridge Testing

Zhimin ZHOU , Yong ZHOU , Mingjun WANG , Chunsheng YANG , Ji'an CHEN , Wen DING , Xiaoyu GAO , Taihua ZHANG

材料科学技术（英）

Microbridge testing was used to measure the Young's modulus and residual stress of metallic films. Samples of freestanding NiFe film microbridge were fabricated by microelectromechanical systems. Special ceramic shaft structure was designed to solve the problem of getting the load-deflection curve of NiFe film microbridge by the Nanoindenter XP system with normal Berkovich probe. Theoretical analysis of load-deflection curves of the microbridges was proposed to evaluate the Young's modulus and residual stress of the films simultaneously. The calculated results based on experimental measurements show that the average Young's modulus and residual stress for the electroplated NiFe films are 203.2 GPa and 333.0 MPa, respectively, while the Young's modulus measured by the Nano-hardness method is 209.6±11.8 GPa for the thick NiFe film with silicon substrate.

关键词: Mechanical properties , 金属薄膜 , 纳米压痕

Theoretical study of the electron paramagnetic resonance parameters and local structure for the tetragonal Ir(2+) centre in NaCl

Pramana-Journal of Physics

The electron paramagnetic resonance (EPR) parameters (the g factors, hyperfine structure constants and the superhyperfine parameters) for the tetragonal Ir(2+) centre in NaCl are theoretically investigated from the perturbation formulas of these parameters for a 5d(7) ion in tetragonally elongated octahedra. This impurity centre is attributed to the substitutional [IrCl(6)](4-) cluster on host Na(+) site, associated with the 4% relative elongation along the C (4)-axis due to the Jahn-Teller effect. Despite the ionicity of host NaCl, the [IrCl(6)](4-) cluster still exhibits moderate covalency and then the ligand orbital and spin-orbit coupling contributions should be taken into account. In addition, the theoretical EPR parameters based on the Jahn-Teller elongation show good agreement with the observed values.

关键词: Electron paramagnetic resonance;crystal- and ligand-field theory;Ir(2+);NaCl;transition-metal ions;epr spectroscopic investigations;atomic;screening constants;nuclear double-resonance;magnetic-resonance;superposition model;silver-halides;spin-resonance;scf functions;complexes

Theoretical studies of EPR parameters and microstructure of the rhombic Co2+-V-Ag centre in AgCl

Physica Status Solidi B-Basic Research

The perturbation formulae of EPR g-factors g(i) (i = x, y, z) and hyperfine constants Ai for a 3d(7) (Co2+) ion at a rhombic octahedral site in a crystal are established from a cluster approach. In these formulae, the contributions from the covalency effect, the configuration interaction and the rhombic crystal field are considered and the parameters used in the calculation of EPR parameters. except the core polarization constant x in the calculation of Al, can be estimated from the optical spectra and the structure data of the studied system. From these formulae, the EPR parameters g(i) and A(i) for the rhombic Co2+-V-Ag centre in AgCl are reasonably explained by considering suitable rhombic distortion and so the microstructure of this rhombic centre is obtained.

关键词: superposition model;crystals

Theoretical investigations of the g-factors and hyperfine structure constants for a tetragonal Co2+ centre in NH4Cl crystal

Physica Status Solidi B-Basic Research

The EPR g-factors g(\\), g(perpendicular to) and hyperfine structure constants A(\\), A(perpendicular to) for a tetragonal Co2+ centre, i.e.. Co(H2O)(2)Cl-4 centre, in NH4Cl crystal are calculated from the perturbation formulas based on a cluster approach. In these formulas, the parameters related to the contributions from the configuration interaction. the covalency effect and the low-symmetry crystal field can be obtained from the optical spectra and the structural model and data of the studied system. The core polarization constant it in the calculation formulas of hyperfine constants is used as an adjustable parameter. The calculated results are in good agreement with the observed values.

关键词: superposition model;centers;resonance;ions;cr3+

NUMERICAL SIMULATION OF ULTRASONIC NON-DESTRUCTIVE TESTING FOR WELDS

H.D. Chen , Y.W. Wang , J. Xue

金属学报(英文版)

A computer simulation technique for ultrasonic propagation is utilized for the simulation of ultrasonic nondestructive testing (NDT). In this paper, one goal of the simulation is to compute ultrasoniceld radiated by arbitrary transducers into pieces under examination. The other simulates a testing experiment. The simulation approach is based on the model for the computation of the ultrasoniceld in isotropic media radiated from actual NDT transducers. After the eld is known, remaining to be modeled is the interaction between this eld and the scatters (defect) and the echo structure. The model of beam-defect interaction is based on the Kirchho's diffraction approximations theory applied to elastodynamics. We assumed that the incident wave fronts on the defect are plane in the case of a focused immersed transducer and material is isotropic and homogeneous. The simulating results demonstrate that the model in ultrasonic NDT of welds is practical in further research and useful in optimizing testing congurations.

关键词: ultrasonic testing , null , null , null

Determination of tensile strength distribution of nanotubes from testing of nanotube bundles

Composites Science and Technology

Single-walled carbon nanotube (SWNT) bundles are subject to tensile testing using a self-developed nano-mechanical testing device. The tensile strength of SWNT bundles, as well as reported data of multi-walled carbon nanotubes (MWNTs) and SWNT ropes, are studied by statistical approach. It is shown that the tensile strength distributions of carbon nanotubes (CNTs) or SWNT ropes can be adequately described by a two-parameter Weibull model. Considering the nonlinear elastic behavior of CNTs, a relation between individual CNT and CNT bundle strengths is studied, and a method for determining the tensile strength distribution of individual CNTs or CNT sub-bundles from experimental measurements on CNT bundles is proposed. Therefore the process for determining the strength distributions of individual CNTs can be greatly simplified by testing CNT bundles instead. (C) 2007 Elsevier Ltd. All rights reserved.

关键词: Carbon nanotubes;Tensile strength;Stress-strain curves;Non-linear;behavior;multiwalled carbon nanotubes;fiber-bundles;hydrocarbons