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Amorphous Metals - Preparation by a Melt-Spinning Method

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Formal Metadata

Title Amorphous Metals - Preparation by a Melt-Spinning Method
Alternative Title Amorphe Metalle - Herstellung nach dem Schmelzspinnverfahren
Author Freyhardt, Herbert C.
Plischke, Dieter
License No Open Access License:
German copyright law applies. This film may be used for your own use but it may not be distributed via the internet or passed on to external parties.
DOI 10.3203/IWF/C-1628eng
IWF Signature C 1628
Publisher IWF (Göttingen)
Release Date 1987
Language English
Producer IWF
Production Year 1986

Technical Metadata

IWF Technical Data Film, 16 mm, LT, 132 m ; F, 12 min

Content Metadata

Subject Area Physics
Abstract The structure of amorphic metals is explained using models. The melt-spinning method for making flash-cooled metallic glass is shown. Time-distorted sequences clarify the melt-spinning method, especially the fusion of several melt-jets.
Keywords amorphic metals
amorphous metal
melt spinning method
metallic glasses
metal physics
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Transcript
The random motion of these spheres is reminiscent of the violent thermal excitation of molecules. It is characterised by the structural disorder which is typical of gases and in the denser case of liquids. The question is: can we freeze this random disorder? In most solid materials solidification results in crystal formation, the right. Metals almost invariably i.e., areas of high order such as we see on behave in this way. Only a few materials, such as glass for example, are amorphous molecularly ordered in the solid state; as shown on the left. The reasons for this amorphous structure are the particular binding forces amongst the atoms involved and the type of
cooling. Hence amorphous metals are made from alloys, particularly with transition metals. Monatomic metals are unsuitable. Moreover, the high quenching speed will prevent crystal formation. So, amorphous metals do not exhibit a regular crystal structure. For this reason they are also called metallic glasses. Technologically they are now becoming more and more important. The common manufacturing procedure to produce thin metallic ribbons is known as melt spinning. Amorphous metals exhibit
a number of advantageous properties, such as for example soft magnetic behaviour or high mechanical strength. How do we set about making such ribbons? One important component of a melt spinner is a crucible made of boron nitride in which the metallic alloy is melted.
Through one or a larger number of nozzles in the bottom plate of the crucible the melt is then forced out and very rapidly cooled down. The surface and width of the metallic ribbon depend on the arrangement of these nozzles. We obtain much narrower ribbons for example from crucibles with only one nozzle than those provided with rows of
nozzles. One of the subjects of this film is to investigate the possibility of producing wider ribbons by different configurations of nozzle rows. But first let us consider the basics of the melt-spinning process itself. The illustration shows the underlying principles of the unit: in the middle a copper drum, which is designed to absorb a major part of the heat of fusion released on quenching. It is set in rapid rotation by an outside electricmotor. Induction heating equipment - supplied by a high-frequency generator melts the alloy in the crucible. Boron nitride permits melting temperatures as high as 2000 Grad Celsius. If pressure is now applied to the melt to force it out of the nozzles in the bottom plate of the crucible on to the rotating copper drum, then the melt remains - as a liquid - for a short instant on the surface of the drum before solidifying very rapidly in the
melt puddle and lifting off the drum as a ribbon of amorphous metal, 20 to 50 micrometer thick. One essential factor is that the quenching
speed is fast enough; depending on the alloy, anything between 1000 and several million degrees per second. The melt should impinge on the drum in laminar flow and at an angle which permits the formation
of a coherent ribbon of constant thickness. Here is a
melt-spinning set-up like the one in use at the "Kristall-Labor" of the Göttingen University Institutes of Physics. The lower section consits mainly of a high-vacuum
pump and the upper part of a vacuum chamber in which the actual process takes place. On the large flange on the left a tube is mounted during the actual
experiment to catch the ribbons. A window is provided in the middle of the chamber for observation purposes. For positioning the melting crucible the lid of the chamber has already been removed. The crucible is screwed into its holder. Through
the upper hose inert gas is pumped in to drive
out the melt under pressure. The two lower hoses are for the cooling water of the holder. Now the crucible is lowered into the high-frequency coil and adjusted with respect to the copper drum. The mechanically polished copper drum is
driven from outside the vacuum chamber via a rotary feedthrough.
After assembly the vacuum chamber is sealed and the chamber is pumped down to a
pressure of 10^-5 mbar - at first by means of a mechanical roughing pump and subsequently by an oil-diffusion pump. Now the apparatus is ready to go. We now observe the actual melt-spinning process from the viewpoint of the window. The copper drum is already rotating at a circumferential speed of 50m/sec. Now the alloy in the crucible is inductively melted and forced out. In real time the process is so brief that the ribbon can hardly be seen. Therefore we repeat the same scene holding the moment of ribbon formation. The contents of the crucible, consisting of several grams of alloy, produce a ribbon several meters in length .And
now let us observe the process in slow motion. The first droplets announce the beginning flow of the melt and now the melt jets: stabilise. They impinge on the copper drum and unite to form the so-called"melt puddle". From this the rotating drum extracts a ribbon to the left, which then lifts off the drum. As the catching tube was dismounted for the purpose of this experiment, the ribbon flies around freely in the vacuum chamber and by pure chance is cut by the melt jets. In the next experimental run, the process is observed
from the point of view of the catching tube. The crucible is reflected in the polished surface of the copper drum. As soon as the melt jets hit the drum, they form a ribbon. A mark on the left hand side of the drum revolving at about 100 revs per second gives a good indication of the speed of the event. Another experimental run from the same viewpoint. The drum has only been polished in the central area to improve adhesion. In this experiment we can clearly see the melt jets coalescing and also how individual jets exhibit momentary turbulence. Holes in the melt cause subsequent holes in the ribbon.
The film was shot at about 8000 frames per second, which enables us to gain good insights into the process events. And now a sequence with an unpolished drum. The aim was to eliminate reflections and thus to get a better view of the surface of the ribbon. Although the adhesive strength of the drum was thereby reduced, an almost ideally shaped ribbon was nevertheless produced. This was an unexpected result because adhesion is responsible for good heat transfer to the copper drum and thus for obtaining the required high quenching speed of the melt. The next trial run proves that under such conditions a ribbon often fails to form at all. Here the drum is also matted overall. Moreover
the melt jets do not flow very well, and on account of the low adhesion no satisfactory melt puddle can be formed. The melt therefore is not cooled sufficiently fast and flies off as droplets throughout the vacuum chamber. In due course the droplets assume spherical shapes and occasionally they can be seen to coalesce. The experiments shown here in laboratory scale provide insights into ways of manufacturing ribbons of moderate width by uniting a number of melt jets. In all the experiments an iron-nickel-boron alloy was used. On industrial scale, using modified equipments, metallic glasses could be manufactured for a wide variety of applications, principally for magnetic purposes.
Liquid
Mental disorder
Geokorona
Order and disorder (physics)
Crystal structure
Force
Crystallization
Glass
Excited state
Metal
Density
Solid
Cartridge (firearms)
Atomism
Material
Metal
Cooling tower
Crystal structure
Electronic component
Koerzitivfeldstärke
Crystallization
Pressure
Prozessleittechnik
Liquid
Elektronenschale
Electric generator
Drum brake
Plating
Spare part
Rotation
Temperature
Nozzle
Measurement
Induktive Erwärmung
Gradient
Watercraft rowing
Angle of attack
Formation flying
Alcohol proof
Micrometer
Laminar flow
Scouting
Coherence (signal processing)
Prozessleittechnik
Pump
Spare part
Vakuumphysik
Astronomisches Fenster
Pressure
Tesla-Transformator
Wasserkühlung
Hose (tubing)
Vakuumphysik
Pressure
Vertical stabilizer
Prozessleittechnik
Regentropfen
Extraction of petroleum
Jet (lignite)
Formation flying
Pump
Vakuumphysik
Fire apparatus
Metre
Separation process
Drum brake
Volumetric flow rate
Astronomisches Fenster
Magnetic moment
Black hole
Prozessleittechnik
Drum brake
Frame rate
Jet (lignite)
Field strength
Refractive index
Atmosphärische Turbulenz
Ground station
Melting
Reflexionskoeffizient
Regentropfen
Jet (lignite)
Scale (map)
Vakuumphysik
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AV-Portal 3.8.2 (0bb840d79881f4e1b2f2d6f66c37060441d4bb2e)