Berlin 2018 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 69: Structural Materials (Steels, light-weight materials, high-temperature materials)

MM 69.4: Talk

Friday, March 16, 2018, 10:15–10:30, H 0106

Theoretical and experimental investigation of mixing and clustering thermodynamics of Ti1-xAlxB2 alloys with age-hardening potential — •Erik Johansson, Nils Nedfors, Annop Ektarawong, Johanna Rosén, and Björn Alling — Linköping University - The Department of Physics, Chemistry and Biology (IFM)

Our project investigates phase stability and temperature dependence of structural parameters of Ti1-xAlxB2 metastable ceramic alloys. These alloys were predicted to exhibit a tendency for isostructural decomposition despite the fact that binary TiB2 and AlB2 are structurally very similar. Due to the reported high hardness of TiB2 and the prospect of age-hardening through isostructural clustering, these alloys could be good candidates for hard protective coatings on industrial cutting tools. In our work, we present theoretical predictions based on first-principles density functional theory. The phase diagram for this ternary system is derived and shows an isostructural miscibility gap. Phonon vibrational contributions to the free energies within harmonic and quasiharmonic approximations are calculated for the ordered binaries and disordered alloys, and we show their effect on the phase diagram. Non-isotropic thermal expansion beyond the standard implementation of the quasiharmonic approximation is investigated, and we discuss the methodological differences. Experimental synthesis of Ti1-xAlxB2 thin films using physical vapour deposition demonstrates the feasibility of growing the alloys, and after heat treatments at 1000 °C isostructural decomposition can be observed in the films confirming the theoretical predictions.