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A Curious Case of Magnetism

Cutting tools are made of a very hard type of material, called cemented carbides. Cemented carbide materials contain grains of carbide (carbon tungsten) that are essentially “glued” together by cobalt atoms. In the process of making cemented carbides, some carbon atoms from the carbide go into the glue (cobalt).

One of the key aspects in the production of cemented carbides is to know the amount of carbon required in the glue to ensure that the cemented carbide has the right qualities. In the production of cemented carbide tools, researchers measure the magnetization of the tool in order to know how much carbon is in the glue. This is a non-destructive quality control.

Figure: an artistic representation of electrons in a material carrying a spin, which is represented by an arrow in the figure.

Magnetism is a complex phenomenon, but in simple worlds, one can think of the electrons in a material as small magnets, coming from the mysterious electronic spin. The more electrons that carry a spin that is pointing in the same direction then the larger the magnetization of the material.

Cobalt is a natural magnet, like iron or a lodestone, and therefore when researchers measure the magnetization in cemented carbides they obtain a signal from the cobalt atoms. However, the presence of carbon changes this magnetic response. Accordingly, by comparing the magnetic responses of pure cobalt with the cemented carbide that contains cobalt with carbon in the glue, the amount of carbon in the tools can be determined. This is the curious case of using a magnetic property like magnetization to actually determine the amount of carbon in a material!

Using Quantum Mechanical calculations, we are able to calculate the magnetization of any material we can think of. We do this by modeling our material system, in this case the cemented carbide. By using quantum information, the spin of the electrons, we can therefore determine the magnetism of the material and thereby predict the amount of carbon in the final product. Moreover, we can change the cobalt atoms by another material in our models, then go on to calculate the magnetization of that new material in order to evaluate if this new candidate has the same magnetic signal – helping the search for a replacement of the glue in the cemented carbide materials.

Indeed, researchers are using the possibilities enabled by quantum computational modeling to determine the macroscopial properties of tools – and using this information to control the quality of cemented carbide tools that are manufactured in industrial processes.

This is a collaboration between Kungliga Tekniska Högskolan (The Royal Institute of Technology,  KTH) and Sandvik Coromant. It is an ongoing project that has not been yet published.

For more information contact:

Raquel Lizárraga
Coordinator of QM-FORMa

Researcher
Unit of Properties
Department of Materials Science and Engineering
Royal Institute of Technology (KTH)
Brinellvägen 23, SE-10044 Stockholm, Sweden

Phone: 070 593 77 56
Email: raqli@kth.se

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