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MM: Fachverband Metall- und Materialphysik

MM 20: Topical Session Designing Innovative Structural Materials and Steels VI

MM 20.5: Vortrag

Dienstag, 23. März 2010, 12:30–12:45, H4

Entropic stabilisation of topologically close-packed phases in binary transition-metal alloys — •Thomas Hammerschmidt¹, Bernhard Seiser², Suzana G. Fries¹, Ingo Steinbach¹, Ralf Drautz¹, and David G. Pettifor² — ¹ICAMS, Ruhr-Universität Bochum, Bochum, Germany — ²Department of Materials, University of Oxford, Oxford, United Kingdom

The formation of topologically close-packed (tcp) phases in Ni-based superalloys leads to the degradation of the mechanical properties of the alloys. The precipitation of the tcp phases is attributed to refractory elements that are added in low concentration to improve creep resistance. It is well known that the structural stability of the tcp phases A15, σ and χ is driven by the average d-band filling. For a direct comparison to experimental phase diagrams, we carried out extensive density-functional theory (DFT) calculations of the tcp phases A15, C14, C15, C36, µ, σ, and χ in tcp-forming binary transition-metal (TM) systems. We observe several systems such as W-Re with positive values of the heat of formation for all tcp phases although some of the phases are observed experimentally. By combining our DFT total energies with the CALPHAD methodology, we can demonstrate that configurational entropy can stabilise the tcp phases in these systems.