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Directional solidification

About: Directional solidification is a(n) research topic. Over the lifetime, 6177 publication(s) have been published within this topic receiving 90781 citation(s).

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Abstract: Several common modes of crystal growth provide particularly simple and elegant examples of spontaneous pattern formation in nature. Phenomena of interest here are those in which an advancing nonfaceted solidification front suffers an instability and subsequently reorganizes itself into a more complex mode of behavior. The purpose of this essay is to examine several such situations and, in doing this, to identify a few new theoretical ideas and a larger number of outstanding problems. The systems studied are those in which solidification is controlled entirely by a single diffusion process, either the flow of latent heat away from a moving interface or the analogous redistribution of chemical constituents. Convective effects are ignored, as are most effects of crystalline anisotropy. The linear theory of the Mullins-Sekerka instability is reviewed for simple planar and spherical cases and also for a special model of directional solidification. These techniques are then extended to the case of a freely growing dendrite, and it is shown how this analysis leads to an understanding of sidebranching and tip-splitting instabilities. A marginal-stability hypothesis is introduced; and it is argued that this intrinsically nonlinear theory, if valid, permits aone to use results of linear-stability analysis to predict dendritic growth rates. The review concludes with a discussion of nonlinear effects in directional solidication. The nonplanar, cellular interfaces which emerge in this situation have much in common with convection patterns in hydrodynamics. The cellular stability problem is discussed briefly, and some preliminary attempts to do calculations in the strongly nonlinear regime are summarized.

1,891 citations

Journal ArticleDOI
J.D. Hunt1
Abstract: An analysis is presented for the growth of equiaxed grains ahead of the columnar front during directional solidification The model considers both single-phase and eutectic equiaxed growth A simple expression is obtained which predicts when fully equiaxed structures should occur It is suggested that the model provides a basis for qualitatively discussing equiaxed growth in more complicated casting situations The effect of equiaxed growth on eutectic spacing is also discussed

881 citations

Journal ArticleDOI
Abstract: In this paper, a general framework is proposed to relate tip radius, interface undercooling and primary arm spacing in alloy dendrite growth. All the growth morphologies (pox, cells, dendrites) developed between the limiting morphology at low and at high velocity: the plane front, are described to a first approximation, using an ellipsoid of revolution. In order to keep the model tractable and the solutions analytic, substantial simplifications are made. It seems nevertheless that this still permits a semi-quantitative prediction of the above-mentioned characteristics for alloy growth in a positive temperature gradient (as in the case of columnar growth or directional solidification).

816 citations

Journal ArticleDOI
Abstract: Melt‐textured growth of polycrystalline YBa2Cu3O7−δ superconductor using directional solidification created an essentially 100% dense structure consisting of long, needle‐ or plate‐shaped crystals preferentially aligned parallel to the a‐b conduction plane. The new microstructure, which completely replaces the previous granular and random structure in the sintered precursor, exhibits dramatically improved transport Jc values at 77 K of ∼17 000 A/cm2 in zero field and ∼4000 A/cm2 at H=1 T (as compared to ∼500 and ∼1 A/cm2, respectively, for the as‐sintered structure), with the severe field dependence of Jc (‘‘weak‐link’’ problem) no longer evident in the new melt‐textured material. The improvement in Jc is attributed to the combined effects of densification, alignment of crystals, and formation of cleaner grain boundaries. Microstructure and distribution of various phases present in the melt‐textured material are discussed in relation to the superconducting properties.

740 citations

Journal ArticleDOI
Abstract: The formation of regular patterns is a common feature of many solidification processes involving cast materials. We describe here how regular patterns can be obtained in porous alumina by controlling the freezing of ceramic slurries followed by subsequent ice sublimation and sintering, leading to multilayered porous alumina structures with homogeneous and well-defined architecture. We discuss the relationships between the experimental results, the physics of ice, and the interaction between inert particles and the solidification front during directional freezing. The anisotropic interface kinetics of ice leads to numerous specific morphological features in the structure. The structures obtained here could have numerous applications, including ceramic filters and biomaterials, and could be the basis for dense multilayered composites after infiltration with a selected second phase.

598 citations

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