Berlin 2008 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 42: Phase Transitions III
MM 42.1: Vortrag
Donnerstag, 28. Februar 2008, 14:00–14:15, H 0107
Stress Induced Martensite in Epitaxial Ni-Mn-Ga Films — •Michael Thomas1,2, Jörg Buschbeck1, Oleg Heczko1, Ludwig Schultz1,2, and Sebastian Fähler1,2 — 1IFW Dresden, P.O. Box: 270116, 01171 Dresden, Germany — 2Institute for Solid State Physics, Department of Physics, Dresden University of Technology, 01062 Dresden, Germany
Martensitic epitaxial Ni-Mn-Ga films with a thickness of about 500 nm were deposited at different temperatures on MgO(001) substrates. Some films are in an orthorhombic martensite state at room temperature though their compositions suggest far lower martensitic transformation temperatures. The martensite transformation is stress induced which was confirmed by X-ray stress analysis. The film structure can be explained as having an austenite layer at the interface between film and substrate. A hierarchical twinned martensite phase is grown on this austenite layer separated by a (101)-habit plane. The distribution of the twin boundaries is controlled by the stress state arising from the substrate constraint. Additionally non-modulated Ni-Mn-Ga films with a tetragonal phase and a coexisting cubic austenite phase were grown. Peeling this films off the substrate leads to the vanishing of the residual austenite phase. The strongly acting stress during the peeling may induce a fully tetragonal non-modulated martensite phase.