Metal founding – Process – Disposition of a gaseous or projected particulate molten...
Patent
1994-02-28
1996-11-12
Batten, Jr., J. Reed
Metal founding
Process
Disposition of a gaseous or projected particulate molten...
164423, 164429, 164444, 164461, 164463, 164479, 164486, B22D 1106, B22D 2300, B22D 2704
Patent
active
055730566
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process and device for the manufacture of strip and composite bodies of metal in which a stream or streams of overheated metal melt is/are directed towards a surface moving transversely to the stream direction, producing an initially liquid metal film.
2. Discussion of the Prior Art
Processes for the rapid solidification of metals have recently gained increasing importance, since they permit the manufacture of new types of materials having partly improved or even unusual structures and, consequently, material properties. With an increasing solidification rate, an ever increasing deviation from the equilibria as determined by the equilibrium diagram occurs as a result, since the extremely short diffusion times impede the appearance of these equilibria. This leads on the one hand to continually finer morphology, e.g. to the development of finer dendrites or eutectics while the interdendritic or cellular segregation is reduced and in some materials can lead to the development of highly metastable structures and even to the formation of metallic glasses in an exceptional case. During the crystalline solidification there is an advantage here in the fact that the solubility range of certain desired elements is greatly widened, whereas undesirable precipitations can be suppressed.
The fundamental principle of all processes for rapid solidification is rapid heat extraction. This action is determined on the one hand by the thermal conductivity of the metal and on the other hand by the mechanism of heat transfer at the phase boundary to the heat-extracting medium. Whereas the heat transfer, characterised by the heat transfer coefficient, can be optimised in a wide range by selecting the correct process conditions, the heat transport in the metal, which is characterised by the coefficient of thermal conductivity, can only be improved by the selection of shorter transport paths. Therefore all currently known methods of rapid solidification lead to castings which have only a small thickness at least in the spatial direction of the heat transport. Examples of this are splat cooling, where a metal drop is abruptly transformed into a foil between two metal plates, the melt-spinning process, where a metal stream is usually applied to the outer surface of a rapidly rotating roll, a thin metal film being formed in a continuous manner under the effect of the acceleration as well as by the heat extraction of the roll, which serves as a quenching body, and certain powder-atomising processes, where a metal stream is beaten into small drops under the effect of an atomising medium which can be a gas or even a liquid, which drops solidify in flight and can subsequently be fed to powder-metallurgical compacting processes. The theoretical principles of processes for rapid solidification are clearly described, for example, in a publication by R. Mehrabian, "Rapid Solidification", reproduced in "Rapid Solidification Technology Source Book", American Society for Metals 1983, pp. 186-209. The most common processes can be gathered from chapters by G. Haour, H. Bode, "From Melt to Wire", and R. E. Maringer, "Payoff Decade for Advanced Material", from the same book, pp. 111-120 and pp. 121-128.
In the processes of spray compacting it is possible to produce larger cast structures, in which case semi-finished products can be produced in dimensions close to the final contours at higher cooling rates. Here, a melt, as a rule overheated by 50-150 K above the liquidus temperature, is usually atomised by means of argon or nitrogen as is the case in powder manufacture. During flight, a substantial portion of the excess heat is taken from the drops by the atomising gas so that the drops--in accordance with their size--strike the substrate in a more or less partially liquid state and weld there to the material deposited beforehand. The process is in principle suitable for the manufacture of flat products, but in particular for the production of rotationally symmetric se
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Feichtinger Derek H.
Feichtinger Heinrich K.
Speidel Markus O.
Batten, Jr. J. Reed
Feichtinger Ilse H.
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