Steady state columnar and equiaxed growth of dendrites and eutectic
TL;DR: In this article, an analysis for the growth of equiaxed grains ahead of the columnar front during directional solidification is presented, and the model considers both single-phase and eutectic growth.
About: This article is published in Materials Science and Engineering.The article was published on 1984-07-01. It has received 1062 citations till now. The article focuses on the topics: Equiaxed crystals & Directional solidification.
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TL;DR: A review of the emerging research on additive manufacturing of metallic materials is provided in this article, which provides a comprehensive overview of the physical processes and the underlying science of metallurgical structure and properties of the deposited parts.
4,192 citations
TL;DR: In this article, a review of additive manufacturing (AM) techniques for producing metal parts are explored, with a focus on the science of metal AM: processing defects, heat transfer, solidification, solid-state precipitation, mechanical properties and post-processing metallurgy.
Abstract: Additive manufacturing (AM), widely known as 3D printing, is a method of manufacturing that forms parts from powder, wire or sheets in a process that proceeds layer by layer. Many techniques (using many different names) have been developed to accomplish this via melting or solid-state joining. In this review, these techniques for producing metal parts are explored, with a focus on the science of metal AM: processing defects, heat transfer, solidification, solid-state precipitation, mechanical properties and post-processing metallurgy. The various metal AM techniques are compared, with analysis of the strengths and limitations of each. Only a few alloys have been developed for commercial production, but recent efforts are presented as a path for the ongoing development of new materials for AM processes.
1,713 citations
TL;DR: The approach to metal-based additive manufacturing is applicable to a wide range of alloys and can be implemented using a range of additive machines, and provides a foundation for broad industrial applicability, including where electron-beam melting or directed-energy-deposition techniques are used instead of selective laser melting.
Abstract: Metal-based additive manufacturing, or three-dimensional (3D) printing, is a potentially disruptive technology across multiple industries, including the aerospace, biomedical and automotive industries. Building up metal components layer by layer increases design freedom and manufacturing flexibility, thereby enabling complex geometries, increased product customization and shorter time to market, while eliminating traditional economy-of-scale constraints. However, currently only a few alloys, the most relevant being AlSi10Mg, TiAl6V4, CoCr and Inconel 718, can be reliably printed; the vast majority of the more than 5,500 alloys in use today cannot be additively manufactured because the melting and solidification dynamics during the printing process lead to intolerable microstructures with large columnar grains and periodic cracks. Here we demonstrate that these issues can be resolved by introducing nanoparticles of nucleants that control solidification during additive manufacturing. We selected the nucleants on the basis of crystallographic information and assembled them onto 7075 and 6061 series aluminium alloy powders. After functionalization with the nucleants, we found that these high-strength aluminium alloys, which were previously incompatible with additive manufacturing, could be processed successfully using selective laser melting. Crack-free, equiaxed (that is, with grains roughly equal in length, width and height), fine-grained microstructures were achieved, resulting in material strengths comparable to that of wrought material. Our approach to metal-based additive manufacturing is applicable to a wide range of alloys and can be implemented using a range of additive machines. It thus provides a foundation for broad industrial applicability, including where electron-beam melting or directed-energy-deposition techniques are used instead of selective laser melting, and will enable additive manufacturing of other alloy systems, such as non-weldable nickel superalloys and intermetallics. Furthermore, this technology could be used in conventional processing such as in joining, casting and injection moulding, in which solidification cracking and hot tearing are also common issues.
1,670 citations
TL;DR: An overview of the phase-field method for modeling solidification is presented, together with several example results as mentioned in this paper, which has been applied to a wide variety of problems including dendritic, eutectic, and peritectic growth in alloys; and solute trapping during rapid solidification.
Abstract: ▪ Abstract An overview of the phase-field method for modeling solidification is presented, together with several example results. Using a phase-field variable and a corresponding governing equation to describe the state (solid or liquid) in a material as a function of position and time, the diffusion equations for heat and solute can be solved without tracking the liquid-solid interface. The interfacial regions between liquid and solid involve smooth but highly localized variations of the phase-field variable. The method has been applied to a wide variety of problems including dendritic growth in pure materials; dendritic, eutectic, and peritectic growth in alloys; and solute trapping during rapid solidification.
1,431 citations
TL;DR: In this article, the effect of separate solute additions of Al, Zr, Sr, Si, and Ca on grain size of Mg has been investigated, and it was found that Sr had a significant grain refining effect in low-Al containing alloys but a negligible effect on grain sizes in Mg-9Al.
Abstract: The effect of separate solute additions of Al, Zr, Sr, Si, and Ca on grain size of Mg has been investigated. Increasing the Al content in hypoeutectic Mg-Al alloys resulted in a continuous reduction in grain size up to 5 wt pct Al, reaching a relatively constant grain size for higher Al contents (above 5 wt pct). The effect of Sr additions was investigated in both low- and high-Al content magnesium alloys, and it was found that Sr had a significant grain refining effect in low-Al containing alloys but a negligible effect on grain size in Mg-9Al. Additions of Zr, Si, and Ca to pure magnesium resulted in efficient grain refinement. The grain refinement is mainly caused by their growth restriction effects, i.e., constitutional undercooling, during solidification, but the effect of nucleant particles, either introduced with the alloying additions or as secondary phases formed as a result of these additions, may enhance the grain refinement. A brief review of grain refinement of magnesium alloys is included in this article to provide an update on research in this field.
671 citations
References
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Book•
01 Jan 1965
4,036 citations
Book•
01 Jan 1965
TL;DR: In this paper, the authors present a general introduction to the theory of transformation kinetics of real metals, including the formation and evolution of martensitic transformations, as well as a theory of dislocations.
Abstract: Part I General introduction. Formal geometry of crystal lattices. The theory of reaction rates. The thermodynamics of irreversable processes. The structure of real metals. Solids solutions. The theory of dislocations. Polycrystalline aggregates. Diffusion in the solid state. The classical theory of nucleation. Theory of thermally activated growth. Formal theory of transformation kinetics. Part II Growth from the vapour phase. Solidification and melting. Polymorphic Changes. Precipitation from supersaturated solid solution. Eutectoidal transformations. Order-disorder transformations. Recovery recrystalisation and grain growth. Deformation twinning. Characteristics of martensic transformations. Crystallography of martensitic transformations. Kinetics of martensitic transformations. Rapid solidification. Bainite steels. Shape memory alloys.
3,397 citations
TL;DR: In this article, a general framework is proposed to relate tip radius, interface undercooling and primary arm spacing in alloy dendrite growth, and all the growth morphologies developed between the limiting morphology at low and at high velocity are described to a first approximation, using an ellipsoid of revolution.
899 citations
TL;DR: In this article, a theoretical model was developed to explain the variation in cellular or dendritic tip temperatures with velocity and temperature gradient, and it was shown that the undercooling can be considered to arise as a result of build up of average solute concentration ahead of the growth front depending mainly on the imposed temperature gradient.
421 citations
TL;DR: In this paper, it is suggested that the change in Si growth morphology may be the result of non-faceted Si growth at high velocities or in the presence of Na.
Abstract: Quenching experiments have been carried out on cast Al-Si eutectic alloys to show that additions of Na affect both the nucleation and growth of the Si phase. The Na not only changes the growth morphology of the Si from the platelike to the fibrous form but also prevents Si nucleating ahead of the eutectic growth front. It is the latter effect, resulting in a change in the average growth velocity, which is responsible for the much finer spacings and larger undercoolings found in modified cast structures. The mechanism for the change in Si growth morphology is discussed and it is suggested that the change may be the result of non-faceted Si growth at high velocities or in the presence of Na.
144 citations