W. Chen
,
D. Fergson and H. Ferguson (Dynamic Systems Inc. Poestenkill
,
NY 12140
,
USA)
金属学报(英文版)
There is a considerable interest in developing methods for processing of materials with ultrafine grain si- zes. Widely used methods in refining microstructure are severe/intense plastic deformation techniques, such as torsion straining, equal channel angular (ECA) pressing/extrusion,and accumulative roll bonding (ARB) technique.While the torsion technique has been available for decades,a new torsion system has been developed at DSI for simulation of complex stress states such as combination of shear and compression or shear and tension stress states. The equal channel angular pressing technique is ma- inly used for production of ultrafine grain aluminum alloys,which is aimed at develoment of high strain rate superplasticity.The accumulative roll bonding technique has been applied for the rolling of both aluminum alloy and steels to produce ultrafine gained materials. Three different types of hot compression deformation methods, each with a different number of deforma- tion axis, are introduced in this paper. They are single axis deformation, two axis deformation and three axis deformation.The single axis deformation has us or little restraint such as plane strain type testing and axisymmetric compression testing, the two - axis deformation can be fully restrained or un- restrained, and the three - axis deformation has no restraint. The two - axis restrainsd compression deformation techopue is recommended for loboratory side after comparing the single - axis and the three - axis deformation techniques since the bulk volume of the two - axis restraint compression speci- men can be easily machined into mechanical testing speciments for mechanical property measurement and other studies,and the technique can be aplied to studies of any metallic materials.
关键词:
ultrafine grain
,
null
Journal De Physique Iv
The disordered systems are of fractal structures. Alexander and Orbach showed that the vibrational density of states for fractal nets follow. the universal law:D(omega) similar to omega(2-:) where d is the spectral (fracton) dimensionality;d=4/3 for any Euclidean dimension d. The excitations belonging to this class were named ''fractons''. We have employed a novel numerical method developed by Williams er al. and performed computer simulation. We have pointed out that the connection between the vibration spectrum and the ultrasonic attenuation in sintered metal powders.
关键词:
fractons
Journal of Magnetism and Magnetic Materials
We investigate the dynamic hysteresis of nanoscale magnetic aggregates by employing Monte Carlo simulation, based on Ising model in non-integer dimensional space. The diffusion-limited aggregation (DLA) model with adjustable sticking probability is used to generate magnetic aggregates with different fractal dimension D. It is revealed that the exponential scaling law A(H(0), omega)similar to H(0)(alpha).omega(beta), where A is the hysteresis area, H(0) and omega the amplitude and frequency of external magnetic field, applies to both the low-omega and high-omega regimes, while exponents alpha and beta decrease with increasing D in the low-omega regime and keep invariant in the high-omega regime. A mean-field approach is developed to explain the simulated results. (C) 2009 Elsevier B.V. All rights reserved.
关键词:
Dynamic hysteresis;Magnetic DLA;Scaling exponent;diffusion-limited aggregation;ising-model;phase-transition;simulation;systems;field
Scripta Materialia
Dynamic strain aging (DSA) in a newly developed Ni-Co superalloy, TMW-2, was examined at temperatures ranging from room temperature to 600 degrees C and strain rates between 3 x 10(-2) and 8 x 10(-5) s(-1). The alloy exhibited both normal and inverse DSA effects at the temperatures and strain rates tested. Transmission electron microscopy evidence suggests that the normal behavior is associated with conventional DSA due to dynamic dislocation-solute interaction, while the inverse behavior may be related to the occurrence of stacking faults. Crown Copyright (C) 2010 Published by Elsevier Ltd. on behalf of Acta Materialia Inc. All rights reserved.
关键词:
Forming processes-forging;Tension test;Nickel alloys;Dynamic strain;aging;alloys;behavior;flow
Materials Characterization
Dendritic coarsening of gamma' was investigated in a directionally solidified Ni-base superalloy during exposure at 1173 K for 24,000 h. Chemical homogeneity along different directions and residual internal strain in the experimental superalloy were measured by electronic probe microanalysis (EPMA) and electron back-scattered diffraction (EBSD) technique. It was indicated that the gradient of element distribution was anisotropic and the inner strain between dendrite core and interdendritic regions was different even after 24,000 h of exposure at 1173 K, which influenced the kinetics for the dendrite coarsening of gamma' phase. (C) 2010 Elsevier Inc. All rights reserved
关键词:
Superalloy;Coarsening;Exposure;Segregation;ni-base superalloy;evolution;field
Chemical Physics Letters
A theoretical method for studying the inter-relation between the local structure and EPR spectra is established by diagonalizing the complete energy matrices. For [M(H(2)O)(6)]XCl(6): Mn(2+) (M = Zn, Mg, Cd, Ca; X = Pt, Sn) systems, the calculated results demonstrate that the local structures around the octahedral Mn(2+) centers in the doped systems are very similar despite of the host crystals being different. Furthermore, it is shown that the EPR zero-field parameter D depends simultaneously on the local structure parameters R and h while (a - F) depends mainly on R, whether the doped systems are at liquid-nitrogen temperature or room temperature. (C) 2008 Elsevier B.V. All rights reserved.
关键词:
electron-paramagnetic-resonance;single-crystals;spectra;field;ions;spectroscopy;copper(ii);complexes;behavior;mn(ii)
Acta Physico-Chimica Sinica
The formation of polymer film of propargyl alcohol(PA) and its protective ability against corrosion in Fe/H2SO4 and Fe/H2SO4 + H2S systems have been investigated using impedance measurement. The composition and morphology of the corrosion surface of iron, on which PA polymerized at different times, were obtained with the aid of SEM and AFM as well as EDX. The results showed that PA polymerized into compact polymer film in Fe/H2SO4 and Fe/H2SO4 + H2S systems, which made iron surface smooth and have a morphologies of regular square structure in microscopic level. In Fe/H2SO4 system, macroscopic continuous polymer film of PA was not formed leading to local corrosion on electrode surface. In Fe/H2SO4 + H2S system, the adsorption of H2S and HS- on electrode surface slowed down the formation of polymer film of PA. However, the iron sulfide, produced after a longer time, increased the continuity of the polymer film of PA and therefore, the polymer film could perform its long-term inhibition action.
关键词:
polymer film of PA;H2S;Fe/H2SO4;inhibition effect;acetylenic alcohols;iron corrosion;adsorption;acid
Chemical Physics Letters
The relationship between the local structure and EPR spectrum is studied by diagonalizing the complete energy matrices for Mn(2+) in a trigonal ligand-field. The results show that the degree of distortion increases with temperature increasing whether it is compressed or elongate distortion, and the distorted tendency of the local structure is different according to the sign of D. Meanwhile, the distortion of Cd(BF(4))(2)center dot 6H(2)O:Mn(2+) system is more sensitive to temperature than that of ZnSnF(6)center dot 6H(2)O:Mn(2+) system. Moreover, the EPR parameter D is closely associated with the local structure parameters R and h while (a - F) is mainly concerned with R. (C) 2010 Elsevier B. V. All rights reserved.
关键词:
single-crystals;optical-absorption;phase-transitions;mn2+;field;ions;resonance;spectra;relaxation;fe-3+
