The metal I thought was glass

This spiral, which appears petrified in the material, has nothing to do with a geological phenomenon … It is the result of a mechanical thermoforming test on mineral glass.

Thermoforming is a forming process used in many fields, which consists of heating a material to soften it, then deforming it by pressing a mould, to make it take the desired shape or pattern. This is what is commonly used to mold plastics, such as food trays.

Metallic glass, on the other hand, is a metallic alloy whose atomic organization is similar to that of glass, which gives it its name. It is produced by very rapid cooling of a liquid metal, thus forming an amorphous substance. The goal is to freeze the structure of the liquid state (with its irregular atoms) before the atoms have had time to organize themselves, or rather to crystallize, as metals traditionally do. Thus, when crystallized solids contain atoms arranged in predictable patterns, amorphous structures have disorganized atoms and lack long-range arrangement. In particular, this makes it possible to obtain Stronger and harder material. The study of hot deformation of this material is the crux of my thesis work.

Just as conventional glass can deform when heated (as shown well by glass blowers and spinners), so can metallic glass deform when raised to a high temperature, here 480°C. The material is then pressed into a mold to reproduce a pattern, like this spiral here.

The only downside to these tests is that mineral glass is more mold resistant! The latter eventually cracks under the applied pressure. So we can see in the photo, in addition to the expected irregular spiral lines, which are simply the cracks of the mold, which were also heat formed on the surface.

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Thermoforming, metallic glass and applications

In general, mineral glass has interesting properties mini apps, for example in biomedicine, watchmaking or microelectronics. Our coil is finally only 6mm wide!

This image, obtained with an optical microscope, reflects the result of one of the first known thermoforming tests on this shade of glass. Its purpose was to determine whether the pattern could be reproduced, and to confirm the choice of parameters or not, such as temperature or speed of deformation of the metallic glass.

Par la suite, de nouveaux motifs pourront être testés afin de modifier les proprietés de surface du matériau, comme le rendre hydrophobe en imitant la morphologie des feuilles de lotus, ou créer des motifs en nid d’abeille pour la améliistorance to cut. Thus the general advantages of mineral glass will be combined with the new surface properties that can be accessed by thermoforming.


This image is one of the winners of the Mécapixel 2021 contest.

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