![]() ![]() See also "Comparison of the Microstructures and Wear Properties of Stellite Nevertheless, the fast growth directions are along. The solid-liquid interface energy is not very anisotropic so the dendrite adopts the smooth shape. The eutectic is a mixture of carbides and matrix. Transmission electron micrograph of a cobalt-rich "blobby" dendrite which is in a hard eutectic (dark). Thus, it is necessary to use transmission electron microscopy to study the fine structure Figure. This is much more expensive than the iron-base alloy described above but is considerably tougher because it has a much finer microstructure. The second example deals with a cobalt-base alloy known as "Stellite". ![]() Photograph by courtesy of Berit Gretoft, Central Research Laboratories, ESAB AB, Sweden. Scanning electron micrograph of a niobium carbide (cubic-F) dendrite in an iron-base hardfacing alloy. The fast growth direction is still Īs can be deduced from the symmetry of the dendrite. In this particular case, the solid/liquid interfacial energy is varies with orientation so the minimum energy shape is that with crystallographic facets. Their shape can be revealed by attacking the sample with an acid which removes the matrix iron-rich phaseįigure. During cooling, niobium carbide dendrites are the first to solidify. The alloy has a chemical composition Fe-34Cr5Nb-4.5C wt.%. Typical applications include earth moving equipment, heavy farm equipment and rock crushers used in the mining industry. We first consider the solidification of a "hardfacing alloy" which is deposited as liquid on substrates which require wear resistance.It is produced in collaboration with colleagues at the Friedrich-Schiller-University Jena It is provided by courtesy of Andreas Schäfer, Chair of Computer Science,įriedrich-Alexander-Universität Erlangen-Nürnberg, Germany. The following video shows how the concentration of copper (in an aluminium 2 wt% copper alloy) in the liquid phase changes as the dendrite solidifies. Growth tends to occur along fast growth directions which are generally for cubic metals. Reichel, Mathematical Modelling of Weld Phenomena III, Institute of Materials, 1997. Photograph courtesy of the Institute of Materials, based on the work of U. The degree of undercooling of the liquid in front of the interface is indicated by the adjacent scale. The simulation is of "free growth", i.e., the solid is growing without contact withĪnything but the liquid. The branching gives it a tree-like character which is the orgin of the term dendrite.Ĭomputer simulated image of the dendritic solidification of pure nickel. The mechanism of this instability is discussed elsewhere.Ī dendrite tends to branch because the interface instability applies at all points along its growth front. The interface thus becomes unstable and in appropriate circumstances solidification becomesĭendritic. The accumulation of solute and heat ahead of the interface can lead toĬircumstances in which the liquid in front of the solidification front is supercooled. Reichel, Mathematical Modelling of Weld Phenomena III, eds H. Similarly, solute may partition into the liquid if its solubility in the solid is less than that in the liquid.Ĭomputer simulated image of dendritic growth using a cellular automata technique. The process may generate heat if the enthalpy of the solid is less than that of the liquid. Once nucleation has occurred, solidification proceeds by the movement of an interface. Alternatively, it may solidify when the pressure is decreased or increased, depending on the sign of the density change. BhadeshiaĪ liquid when cooled solidifies. Dendritic Solidification Dendritic Solidification H. ![]()
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