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1.
Solidification processing 总被引:5,自引:0,他引:5
M. C. Flemings 《Metallurgical and Materials Transactions B》1974,5(10):2121-2134
Interaction between theory and practice in the field of solidification has been strong in recent years, to the great benefit
of both. Solution of important problems has required conceptualizing on greatly different size scales simultaneously, and
has also required extensive experimentation to suggest and justify suitable approximations for theoretical analyses. Some
areas of solidification where theory and practical application have advanced, or are advancing nicely together are dendrite
arm spacing, grain size control, columnar structures, eutectic-like in-situ composites, inclusion formation, macrosegregation,
and non-dendritic structures. 相似文献
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J. S. Langer 《Metallurgical and Materials Transactions A》1984,15(6):961-966
Directional solidification of alloys produces a wide variety of cellular or lamellar structures which, depending upon growth
conditions, may be reproducibly regular or may behave chaotically. It is not well understood how these patterns are selected
and controlled or even whether there ever exist sharp selection mechanisms. A related phenomenon is the spatial propagation
of a pattern into a system which has been caused to become unstable against pattern-forming deformations. This phenomenon
has some features in common with the propagation of sidebranching modes in dendritic solidification. In a class of one-dimensional
models, the nonlinear system can be shown to select the propagating mode in which the leading edge of the pattern is just
marginally stable. This stability principle, when applicable, predicts both the speed of propagation and the geometrical characteristics
of the pattern which forms behind the moving front. A boundary-layer model for fully two or three dimensional solidification
problems appears to exhibit similar mathematical behavior.
This paper is based on a presentation made at the symposium “Establishment of Microstructural Spacing during Dendritic and
Cooperative Growth” held at the annual meeting of the AIME in Atlanta, Georgia on March 7, 1983 under the joint sponsorship
of the ASM-MSD Phase Transformations Committee and the TMS-AIME Solidification Committee. 相似文献
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Solidification in Spray Forming 总被引:1,自引:0,他引:1
P.S. GRANT 《Metallurgical and Materials Transactions A》2007,38(7):1520-1529
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J. J. Coronado A. Sinatora E. Albertin 《Metallurgical and Materials Transactions B》2014,45(3):811-814
Two hypereutectic cast irons (5.01 pct Cr and 5.19 pct V) were cast and the polished surfaces of test pieces were deep-etched and analyzed via scanning electron microscopy. The results show that graphite lamellae intersect the cementite and a thin austenite film nucleates and grows on the cementite plates. For both compositions, graphite and cementite can coexist as equilibrium phases, with the former always nucleating and growing first. The eutectic carbides grow from the austenite dendrites in a direction perpendicular to the primary plates. 相似文献
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M.Suzuki T.J.Piccone M. Flemings H.D. Brody 相似文献
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板坯凝固过程夹杂物运动行为 总被引:1,自引:0,他引:1
本文使用离散相模型,利用数值模拟的方法对结晶器中的钢液流动、传热、凝固以及夹杂物的运动进行了耦合计算。通过追踪夹杂物的运动轨迹,并在钢渣界面处对夹杂物进行采样分析,最终计算出夹杂物在结晶器中的上浮率。研究表明,夹杂物在结晶器中的上浮率与其尺寸及拉速的大小均有关系,但受夹杂物密度的影响很小。夹杂物越大、拉速越小,越有利于夹杂物上浮至自由液面。小颗粒夹杂在结晶器中并不能被有效去除。对于粒径为50μm的夹杂物,当拉速为1m/min时其上浮率仅为46%,有37%的夹杂物被凝固坯壳捕捉,主要分布在铸坯表皮下10~25mm处。夹杂物被宽面坯壳捕捉的位置多集中在宽面靠近窄面处,在水口下方被捕捉的夹杂物较少。以往的研究认为只要夹杂物上浮至钢渣界面就能够被保护渣吸收,J.Strandh等的研究表明,夹杂物能否被吸收还取决于保护渣的粘度和润湿性等因素。因此,对于粒径较小的夹杂物,必须在精炼后的软吹氩过程中适当增大钢液的静置时间,尽量减少钢液中小颗粒夹杂的数量。另外,结晶器保护渣的选用对钢液中夹杂物的去除也很重要,不仅要满足其对钢液的保温润滑作用,还要考虑其对夹杂物吸附的影响。 相似文献
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Vaughan R. Voller 《Transactions of the Indian Institute of Metals》2012,65(6):515-519
A non-local flux, constructed as a weighted sum of local gradients, is introduced into a standard solidification model. A particular choice of weights leads to a flux expressed as a Caputo fractional derivative. Numerical solution, indicates that??in modeling solidification at microstructure scales of?~5?mm??the presence of non-locality influences the distribution of temperature and liquid fraction and also increase the expected exponent in the characteristic solidification time scale. 相似文献
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在金属凝固过程中,对金属液施加各种物理场可以提高铸坯的等轴晶比例,细化凝固组织,从而提高铸坯的力学和物理性能.文章介绍了近年来一些机械法凝固技术的研究现状,并简要指出这些技术的优缺点所在. 相似文献
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袁静 《有色金属材料与工程》2011,32(1):42-44
针对日趋活跃的金属定向凝固技术,阐述定向凝固技术的基本原理,以及其特点.简要说明了金属定向凝固技术的应用.介绍了目前金属定向凝固技术在国内外的发展状况,存在的问题及未来的前景. 相似文献
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The solidification behavior of ceramic particle-reinforced metal-matrix composites (MMCs) is different from that of the bare matrix, not only because of the presence of the ceramic particles, but also due to their redistribution in the melt that results in nonhomogeneous thermophysical properties. The MMCs comprised of 10-to 15-μm SiC particles of varying volume fractions, dispersed uniformly in a modified aluminum A356 alloy by the melt stirring technique, were solidified unidirectionally in a thermocouple-instrumented cylindrical steel mold. The cooling rates were continually monitored by measuring temperatures at different depths in the melt, and the solidified MMCs were sectioned into disks and chemically analyzed for SiC volume fraction. The results point out that the cooling rate increased with increasing volume fraction of SiC particles. A small increase in the bulk SiC volume fraction of the cast MMC was observed due to particle settling during solidification. A one-dimensional enthalpy model of MMC solidification was formulated, wherein particle settling occurring in the solidifying matrix was coupled to the enthalpy equation by means of the Richardson-Zaki hindered settling correlation. A comparative study of simulations with experiments suggested that the thermal response of SiC particles used in this study was similar to that of single crystals, and their presence increased the effective thermal conductivity of the composite. 相似文献
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Solidification of high-speed tool steels 总被引:4,自引:0,他引:4
H. F. Fischmeister R. Riedl S. Karagöz 《Metallurgical and Materials Transactions A》1989,20(10):2133-2148
Gradient solidification and differential thermal analysis (DTA) experiments were used to study the process of solidification
and the solidification microstructure of 11 alloys comprising the composition range of customary commercial high-speed steels
(with the exception of cobalt-alloyed grades). Also included are a number of experimental high-speed steels alloyed with niobium.
The results include the effects of alloy composition and cooling rate on the width of the solidification interval and on the
sequence of the solidification reactions; the types of eutectics formed (austenite with M6C, M2C, or MC) and their volume fractions; the chemical compositions of the ledeburitic and primary carbides; and the relation
between the chemistry of the carbides and that of the melt. Special attention is given to the formation and composition of
heterogeneously nucleated primary MC particles and to the chemistry and stability of eutectic M2C, which is important as a precursor to MC and M6C in the microstructure of finished (hot-worked and heat-treated) material. 相似文献
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The effect of undercooling on grain structure is investigated in pure nickel, Ni75Cu25, and DD3 singlecrystal superalloy by employing the method of molten salt denucleating combined with thermal cycling. Meanwhile,
a comparison of factors that may be related to structure formation is performed and the difference in the refined structure
between Ni75Cu25 alloy and DD3 single-crystal superalloy is explained. Only one grain refinement occurs at the critical undercooling in pure
nickel, whereas two take place at both low and high undercoolings in Ni75Cu25 and DD3 single-crystal superalloy melts. The first grain refinement at low undercoolings mainly originates from dendrite
remelting driven by the chemical superheating produced in recalescence, and the second one at high undercoolings is due to
the recrystallization process as a result of the high stress provided in the rapid solidification after high undercooling.
Dislocation morphology evolution in as-solidified structure is also provided by the transmission electron microscopy (TEM)
technique to further verify the recrystallization mechanism. 相似文献
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1 前言 钢材的组织结构决定了其性能,尤其是强度和韧性.晶粒越细,钢材的强度和韧性就越高.近年来,人们针对细化晶粒组织做了大量的研究,开发了铁素体粒径达1μm的晶粒细化技术,其中主要是形变热处理(TMCP)技术. 相似文献