Atomic-level observations could lead to optimised cutting tools

Researchers have developed a method of observing a common coating used on hard cutting materials it degrades, an advance that could save manufacturers time and money.

The team at Linköping University (LiU) in Sweden have developed a theoretical model that lets them observe the behaviour of titanium-aluminium nitride, a ceramic coating that hardens tools during the cutting process, a phenomenon called age hardening.

The alloy is, however, sensitive to high temperature. At temperatures up to 700 degrees, the material is unharmed, but it starts to degrade at higher temperatures.

Until now, no one has been able to determine what happens at the atomic level inside the thin film during the cutting process. According to LiU, it has only been possible to partially simulate the properties of the complex combination of titanium, aluminium and nitrogen, and it has not been possible to draw any conclusions from the results.

Georgios Almyras, a former post-doctoral researcher at LiU’s Nanoscale Engineering Division, Davide Sangiovanni of the Division of Theoretical Physics, and Kostas Sarakinos, associate professor in materials science at LiU and head of the Nanoscale Engineering Division, have developed a reliable theoretical model that can be used to show exactly what happens in the material, with picosecond time resolution. They have used the newly developed model to simulate events in the material, showing which atoms are displaced and the consequences this has for the properties. The model has been published in Materials.

"This also means that we can develop strategies to stop the degradation, such as alloying the materials or creating specially-designed nanostructures", Sangiovanni said in a statement.

Their theoretical model is said to calculate the forces between the atoms in the material. The model is based on a previously known method that has been successfully used in simple material systems. Complex combinations of materials, however, require time-demanding calculations that are only possible in a supercomputer.

Optimised cutting tools

The supercomputer at the National Supercomputer Centre at LiU has then been used for calculations of around 40 alloys of the three elements titanium, aluminium and nitrogen, while looking at several properties of the material. The scientists then compared the results from the calculations with the known properties of the materials.

"The agreement is very good", said Sarakinos. "It's important that we have calculated also properties that we know, because then we can be sure that the calculations and predictions of the model are reliable."

The researchers hope the method will be useful for companies in the manufacturing industry - such as Sandvik, ABB, and Seco Tools - that the LiU researchers have long-term collaboration agreements with.

"We can now for the first time carry out large-scale classical simulations of atomic structures in one of the material systems most commonly used for metal cutting and forming. The simulations can consider resistance to heat or nanostructures, and they may provide important insight into how the atoms move. The results will help us avoid, or at least delay, degradation of the material", said Sarakinos.

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