Lecture

Solidification Phenomena: Dendrites and Constitutional Supercooling

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In course

MSE-302: Phase transformations

Ce cours est une introduction aux transformations de phases liquide-solide et solide-solide. Il aborde les aspects thermodynamiques et cristallographiques. Il traite principalement des matériaux métalliques, et établira des ponts vers les céramiques et la ...

Description

This lecture covers the solidification processes of pure metals and alloys, focusing on the formation of dendritic structures. It begins with an introduction to solidification, explaining how pure metals typically solidify against a cold mold, leading to planar front growth under specific thermal conditions. In contrast, alloys generally solidify by forming dendrites, with columnar structures at the edges and equiaxed structures at the center. The concept of constitutional supercooling is introduced, highlighting how it affects the stability of the solidification front. The lecture further explores various cases of alloy solidification, including the impact of thermal gradients and diffusion on the solidification process. It discusses experimental setups, such as the Bridgman furnace, to control solidification parameters. The lecture concludes with a summary of the differences in solidification behavior between pure metals and alloys, emphasizing the conditions that lead to stable or unstable growth of solidification fronts.

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Instructor

Cyril Cayron

1992-1995 Engineering School. Ecole des Mines de Nancy. 1994-1995 Master's degree in Materials Science (rank = 1st) 1995-1996 Military Service 1996-2000 PhD at EPFL-CIME. Precipitation in 6xxx alloys and composites. 2000-2014 Researcher, Engineer and Group leader on materials for new energies at CEA-Grenoble, France. 2012 Habilitation to supervise researches (HDR) 2014-now Senior Scientist at EPFL-LMTM Creator of the computer programs GenOVa and ARPGE (in Python). I currently work on crystallographic models of martensitic transformations and deformation twinning.

Official source

Related concepts (32)

Supercooling

Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid below its freezing point without it becoming a solid. It achieves this in the absence of a seed crystal or nucleus around which a crystal structure can form. The supercooling of water can be achieved without any special techniques other than chemical demineralization, down to . Droplets of supercooled water often exist in stratus and cumulus clouds.

Freezing

Freezing is a phase transition where a liquid turns into a solid when its temperature is lowered below its freezing point. In accordance with the internationally established definition, freezing means the solidification phase change of a liquid or the liquid content of a substance, usually due to cooling. For most substances, the melting and freezing points are the same temperature; however, certain substances possess differing solid-liquid transition temperatures. For example, agar displays a hysteresis in its melting point and freezing point.

Thermal conductivity

The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by , , or . Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal conductivity. For instance, metals typically have high thermal conductivity and are very efficient at conducting heat, while the opposite is true for insulating materials like mineral wool or Styrofoam.

Convection (heat transfer)

Convection (or convective heat transfer) is the transfer of heat from one place to another due to the movement of fluid. Although often discussed as a distinct method of heat transfer, convective heat transfer involves the combined processes of conduction (heat diffusion) and advection (heat transfer by bulk fluid flow). Convection is usually the dominant form of heat transfer in liquids and gases. Note that this definition of convection is only applicable in Heat transfer and thermodynamic contexts.

Precious metal

Precious metals are rare, naturally occurring metallic chemical elements of high economic value. Chemically, the precious metals tend to be less reactive than most elements (see noble metal). They are usually ductile and have a high lustre. Historically, precious metals were important as currency but are now regarded mainly as investment and industrial raw materials. Gold, silver, platinum, and palladium each have an ISO 4217 currency code. The best known precious metals are the coinage metals, which are gold and silver.

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