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991.
Nicholas Biery Marc De Graef Jack Beuth Rafel Raban Andrew Elliott Tresa M. Pollock Curt Austin 《Metallurgical and Materials Transactions A》2002,33(10):3127-3136
Tensile experiments have been performed on specimens of four different investment-cast TiAl-based alloys with variations in
casting conditions. The average ductilities obtained in these experiments vary between approximately 0.8 to 2.0 pct plastic
strain to failure in tension. By using the three-parameter form of the Weibull relation, with the 0.2 pct offset yield strength
as the minimum failure strength, the resulting variability in the data can be quantified and is found to be similar for those
alloys with similar microstructural scale (grain size). Large variations in lamellar volume fraction, segregation, and phase
distribution have a minor influence on property variability, compared to changes in the scale of the grain structure caused
by either variations in cooling rate during casting or the addition of grain refiners. 相似文献
992.
1 前言 CONTOP~R工艺最初是由德国科隆的KHDHumboldt Wedag AG公司针对有色金属工业而开发的。两台迄今为止最大的CONTOP~R熔炼旋风炉建于美国德克萨斯的ASARCO公司,每台能力为32t/h铜精矿混和料。 1998年,奥钢联工程技术公司(VAI)获得了 相似文献
993.
Mingjun Li Kosuke Nagashio Ph.D. Kazuhiko Kuribayashi 《Metallurgical and Materials Transactions A》2002,33(8):2677-2683
A mullite (3Al2O3·2SiO2) sample has been levitated and undercooled in an aero-acoustic levitator, so as to investigate the solidification behavior
in a containerless condition. Crystal-growth velocities are measured as a function of melt undercoolings, which increase slowly
with melt undercoolings up to 380 K and then increase quickly when undercoolings exceed 400 K. In order to elucidate the crystal
growth and solidification behavior, the relationship of melt viscosities as a function of melt undercoolings is established
on the basis of the fact that molten mullite melts are fragile, from which the atomic diffusivity is calculated via the Einstein-Stokes equation. The interface kinetics is analyzed when considering atomic diffusivities. The crystal-growth
velocity vs melt undercooling is calculated based on the classical rate theory. Interestingly, two different microstructures are observed;
one exhibits a straight, faceted rod without any branching with melt undercoolings up to 400 K, and the other is a feathery
faceted dendrite when undercoolings exceed 400 K. The formation of these morphologies is discussed, taking into account the
contributions of constitutional and kinetic undercoolings at different bulk undercoolings. 相似文献
994.
J. C. Williams R. G. Baggerly N. E. Paton 《Metallurgical and Materials Transactions A》2002,33(3):837-850
Single crystals of Ti-Al alloys containing 1.4, 2.9, 5, and 6.6 pct Al (by weight) were oriented for 〈a〉 slip on either basal or prism planes or loaded parallel along the c-axis to enforce a nonbasal deformation mode. Most of the tests were conducted in compression and at temperatures between
77 and 1000 K. Trace analysis of prepolished surfaces enabled identification of the twin or slip systems primarily responsible
for deformation. Increasing the deformation temperature, Al content, or both, acted to inhibit secondary twin and slip systems,
thereby increasing the tendency toward strain accommodation by a single slip system having the highest resolved stress. In
the crystals oriented for basal slip, transitions from twinning to multiple slip and, finally, to basal slip occurred with
increasing temperature in the lower-Al-content alloys, whereas for Ti-6.6 pct Al, only basal slip was observed at all temperatures
tested. A comparison of the critically resolved shear stress (CRSS) values for basal and prism slip as a function of Al content
shows that prism slip is favored at room temperature in pure Ti, but the stress to activate these two systems becomes essentially
equal in the Ti-6.6 pct Al crystals over a wide range of temperatures.
Compression tests on crystals oriented so that the load was applied parallel to the c-axis showed extensive twinning in lower Al concentrations and 〈c+a〉 slip at higher Al concentrations, with a mixture of 〈c+a〉 slip and twinning at intermediate compositions. A few tests also were conducted in tension, with the load applied parallel
to the c-axis. In these cases, twinning was observed, and the resolved shear for plastic deformation by twinning was much lower that
that for 〈c+a〉 slip observed in compression loading.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science and Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
995.
996.
A theory related to the statistics of the structure and properties of inhomogeneous materials has been proposed, dealing with the distribution of properties from sampling of inhomogeneous structures by line transects. It is demonstrated that the empirical cumulative distribution functions of the intercepts from the microstructural constituents and their variances are important fingerprints of the inhomogeneous structures.Simulated sampling of the images of the microstructure by line transects has been proposed as a powerful method for characterization the distribution of properties of inhomogeneous structures. One of the advantages of the method based on the expected values of the order statistics of the intercepts is that the probability bounds of the property are determined without prior knowledge of the functional relationship between the property and the intercepts from the structural constituents.The concept intercept variance has an important application in determining the minimum transect length that stabilizes the variation of the intercept at a low value. Additionally, the concept ‘intercept variance’ can be used for topological optimization of the microstructure regarding the risk of intercepting a large amount of the weaker constituent. Equations regarding the variance of the intercepted fraction characterizing transect lengths with a specified distribution have also been derived. 相似文献
997.
998.
999.
1000.
Mohsen A. Issa Mahmoud A. Issa H. Abdalla Md. S. Islam A. Chudnovsky 《Probabilistic Engineering Mechanics》2002,17(2)
In the present work, the distribution of the random toughness characteristics (i.e. critical energy release rate, G1c) has been evaluated on the basis of experimental observations. Fracture test results from three groups of geometrically similar concrete specimens of size (width×total depth×thickness), 420×420×50–1680×1680×200 mm3, made with different maximum aggregate size of 9.5, 19, 38, and 76 mm were analyzed using a recently proposed distribution of extremes. In applications of probability, it is important to use an appropriate distribution type and adequate techniques for estimating the parameters of distribution. In this study, a new type distribution of minima is employed for probability computations. It was noticed that the entropy of distribution increases with the crack length, i.e. the uncertainty of toughness, G1c, value increases with crack length. A non-linear reduction of the maximum allowable splitting force with the defect size, a, was noticed. For large specimens, the maximum allowable splitting load is more sensitive to the required reliability level than that for small specimens. Reliability increases with aggregate size when all other conditions were constant. 相似文献