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Equiaxed crystals

About: Equiaxed crystals is a(n) research topic. Over the lifetime, 5898 publication(s) have been published within this topic receiving 100065 citation(s).

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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: A new approach to the modelling of grain structure formation in solidification processes is proposed. Based upon a two-dimensional cellular automata technique, the model includes the mechanisms of heterogeneous nucleation and of grain growth. Nucleation occurring at the mould wall as well as in the liquid metal are treated by using two distributions of nucleation sites. The location and the crystallographic orientation of the grains are chosen randomly among a large number of cells and a certain number of orientation classes, respectively. The growth kinetics of the dendrite tip and the preferential 〈100〉 growth directions of cubic metals are taken into account. The model is then applied to small specimens of uniform temperature. The columnar-to-equiaxed transition, the selection and extension of columnar grains which occur in the columnar zone and the impingement of equiaxed grains are clearly shown by this technique. The calculated effect of the alloy concentration and cooling rate upon the resultant microstructure agree with experimental observations.

692 citations

Journal ArticleDOI
Abstract: Pure nickel was selected for a detailed investigation of the experimental parameters influencing grain refinement and microstructural evolution during processing by high-pressure torsion (HPT). Samples were examined after HPT using microhardness measurements, transmission electron microscopy and orientation imaging microscopy. Processing by HPT produces a grain size of ~170 nm in pure Ni, and homogeneous and equiaxed microstructures are attained throughout the samples when they are subjected to at least ~5 whole revolutions under applied pressures of at least ~6 GPa. For these conditions, the distributions of grain boundary misorientations are similar in the center and at the periphery of the samples. A simple model is proposed to explain the development of a homogeneous microstructure in HPT.

653 citations

Journal ArticleDOI
Abstract: Grain structure is an important and readily observable feature in cast aluminium alloys. Three different types of grain morphology are possible, namely, columnar, twinned columnar, and equiaxed. Inoculants in the form of master alloys are used to promote the formation of a fully equiaxed grain structure and this is termed grain refinement. Initially, fundamental aspects of solidification are outlined in order that the principles of grain refining using master alloys can be understood. Techniques for the commercial production and testing of common Al–Ti-based master alloys are then discussed briefly. The exact mechanisms by which grain refinement occurs are not yet fully understood and experimental and theoretical studies on the problem are critically reviewed with particular emphasis on (a) the role of solute titanium, (b) the thermodynamics of Al–Ti-based alloy systems, and (c) the nature of heterogeneous nuclei. Finally, current and future trends in the use of grain refining alloys are summarised.

520 citations

Journal ArticleDOI
Abstract: Experiments were conducted to investigate the ultrafine-grained (UFG) microstructures in the surface layer of an aluminum alloy 7075 heavily worked by ultrasonic shot peening. Conventional and high-resolution electron microscopy was performed at various depths of the deformed layer. Results showed that UFG structures were introdued into the surface layer of 62 μm thick. With increasing strain, the various microstructural features, e.g., the dislocation emission source, elongated microbands, dislocation cells, dislocation cell blocks, equiaxed submicro-, and nano-crystal grains etc., were successively produced. The grain subdivision into the subgrains was found to be the main mechanism responsible for grain refinement. The simultaneous evolution of high boundary misorientations was ascribed to the subgrain boundary rotation for accommodating further strains. Formed microstructures were highly nonequilibratory.  2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

382 citations

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