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Ab initio and phenomenological modeling of materials related to CVD hard coatings

Time: Fri 2021-12-10 10.00

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Language: English

Subject area: Materials Science and Engineering

Doctoral student: Axel Forslund , Strukturer

Opponent: Professor Paul Erhart, Condensed Matter and Materials Theory, Department of Physics, Chalmers University of Technology

Supervisor: Professor Andrei V. Ruban, Materialvetenskap, Strukturer

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This thesis describes the work based on two different tools in computational materials science: a first-principles approach, namely that of density functional theory, and the CALPHAD approach.

These two methods were used in this work to calculate properties of materials related to hard coatings, in particular coatings produced with chemical vapor deposition for the purpose of wear protection in cutting tools. Several parts of the work is also, in many aspects, of a general character. In a few cases, the material investigations were performed on simpler demonstration systems, with the intention of further application on more involved material systems.

A variety of different methods and specific applications are included in this thesis. The reaction-diffusion in Ni-base superalloys deposited by vapor deposition methods was simulated with a continuum approach with CALPHAD thermodynamic and kinetic data. CALPHAD models were also used to predict the stable phases for TiN deposition on a CoCrFeNi substrate. Surfaces and segregation energies were investigated in a random alloy, pseudobinary (Al,Ti)N system. This system was also the subject of calculations of formation energies of structural vacancies, and the configurational dependence of these properties was investigated.

Further, surface free energies including all relevant thermal excitations were calculated for TiN(001) and several W surfaces in a newly developed methodology including machine-learning interatomic potentials. For W, the temperature dependence of the surface anisotropy was obtained, which was shown to be decreasing with temperature, with a surface free energy approaching experimental values at the melting temperature.