Dresden 2017 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 49: Microstructure and Phase Transformations - shape memory alloys
MM 49.2: Talk
Wednesday, March 22, 2017, 16:00–16:15, IFW B
Ordering Nanotwins in Modulated Martensite — Markus E. Gruner1,2, Robert Niemann2, Peter Entel1, Rossitza Pentcheva1, Ulrich K. Rössler2, Kornelius Nielsch2, and •Sebastian Fähler2 — 1Theoretical Physics and Center for Nanointegration, CENIDE, University of Duisburg-Essen, D-47048 Duisburg, Germany — 2IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany
Modulated ferromagnetic martensites exhibit outstanding magnetocaloric and magnetic shape memory properties. Focusing on the Ni2MnGa prototype system, we use large scale density functional theory calculations to demonstrate that the formation of modulated martensite and key functional properties are governed by ordering nanotwins. Ordering is driven by the interaction between twin boundaries, which oscillates with the distance between twin boundaries. Minimizing the interaction energy results in the experimentally observed ordered modulations at the atomic scale, it explains a particular type of stacking fault at the mesoscale, known as a/b twin boundaries, and contributes substantially to the macroscopic hysteresis losses. Furthermore, an analysis of the relaxation process reveals that phonon softening paves the way for the transition towards the nanotwinned martensite, which unifies both competing concepts to explain modulated martensite.