Theory of Microstructural Development during Rapid Solidification

Casting alloys of eutectic composition are of great practical importance. Good microstructural control of these alloys is essential in obtaining the required properties in the cast state. P...

Dendrite growth in eutectic alloys: the coupled zone

Dendritic growth is one of the most common microstructures in metal and solution solidification. The subject of dendritic growth has received much attention from both scientific and industrial points of view. On the one hand, dendritic growth has become a deeply investigated subject in non-linear dynamics field. On the other hand, its understanding became essential for some engineering applications, mainly in metallurgy and latent thermal energy storage where phase change materials are used. Therefore, understanding and modeling the mechanisms which result the dendritic structures has been the objective of much research over the last decades. In order to understand the formation of dendrites, it is essential to understand the physical mechanisms on the interface separating the two phases. This paper reviews and discusses the available theories of dendritic growth, and then introduces the Gibbs-Thomson condition which has to be taken into account to handle all interfacial effects. Based on the Gibbs-Thomson condition, a complete mathematical model describing the dendritic growth problem for pure substances is formulated. This model includes the heat equation in both liquid and solid phases, the heat conservation equation at the interface separating these two phases, and the proposed Gibbs-Thomson equation. In order to solve this complex non-linear problem, several numerical methods have been developed. Hence, in its last section, the paper reviews these numerical methods distinguishing between two major classes involving the explicit and the implicit tracking of the moving interface.

A review of dendritic growth during solidification: Mathematical modeling and numerical simulations

A transducer crystal is coupled to a coupling plastic material made of a compression molded polyimid amide. Two cooperating transducer housings are formed of two wedges of material cut from the same rectangular billet. The wedge angle is calculated after measuring the sonic velocity of the billet. A novel buffer is applied to the rear surface of the transducer crystal and consists of an epoxy body having tungsten powder and small particles of an elastomer distributed therein. The transducer body is mounted on a support track which has a similar configuration for numerous different mounting arrangements. The transducer housings are axially spaced from one another along the axis of the pipe and are set to a given spacing by locating a mounting clip on an index plate on the track. Transducers for a portable type application have tracks connected to one another along one of their sides by a flexible but tough sheet of material which fixes the spacing of the tracks for a given pipe diameter. The opposite rails of the two tracks are connected together by a quick release strap arrangement.

Transducer structure and mounting arrangement for transducer structure for clamp-on ultrasonic flowmeters

Laser-wakefield accelerators (LWFAs) are high acceleration-gradient plasma-based particle accelerators capable of producing ultra-relativistic electron beams. Within the strong focusing fields of the wakefield, accelerated electrons undergo betatron oscillations, emitting a bright pulse of X-rays with a micrometer-scale source size that may be used for imaging applications. Non-destructive X-ray phase contrast imaging and tomography of heterogeneous materials can provide insight into their processing, structure, and performance. To demonstrate the imaging capability of X-rays from an LWFA we have examined an irregular eutectic in the aluminum-silicon (Al-Si) system. The lamellar spacing of the Al-Si eutectic microstructure is on the order of a few micrometers, thus requiring high spatial resolution. We present comparisons between the sharpness and spatial resolution in phase contrast images of this eutectic alloy obtained via X-ray phase contrast imaging at the Swiss Light Source (SLS) synchrotron and X-ray projection microscopy via an LWFA source. An upper bound on the resolving power of 2.7 ± 0.3 μm of the LWFA source in this experiment was measured. These results indicate that betatron X-rays from laser wakefield acceleration can provide an alternative to conventional synchrotron sources for high resolution imaging of eutectics and, more broadly, complex microstructures.

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Laser-wakefield accelerators for high-resolution X-ray imaging of complex microstructures

On the growth of the Ni-W eutectic

Device for locating boundaries of non-homogeneous bodies

Relation of Interphase Spacing and Growth Temperature to Growth Velocity in Fe-C and Fe-Fe3C Eutectic Alloys

Morphologie de l'eutectique orienté CoCoAl et influence d'une addition de nickel

A metallic alloy is cast in a mold to produce a solid body by unidirectional solidification. The alloy, initially in a molten state, is cast into a mold and is completely and progressively cooled in the mold while a unidirectional thermal gradient superimposed thereon parallel to a direction determined by the configuration of the mold (predetermined direction) until a metastable equilibrium is reached in which the entire body of the melt is in a super-cooled state as a homogeneous liquid. The equilibrium is then broken to cause solidification of the alloy and the formation of dendritic crystals with their principal axes parallel to the thermal gradient substantially instantly and without noticeable advance of a solidification front across the melt.

Wilfried Kurz

Papers

On the growth of the Ni-W eutectic

Device for locating boundaries of non-homogeneous bodies

Relation of Interphase Spacing and Growth Temperature to Growth Velocity in Fe-C and Fe-Fe3C Eutectic Alloys

Morphologie de l'eutectique orienté CoCoAl et influence d'une addition de nickel

Casting process with instantaneous unidirectional solidification