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MM: Fachverband Metall- und Materialphysik

MM 49: Microstructure and Phase Transformations - shape memory alloys

MM 49.4: Vortrag

Mittwoch, 22. März 2017, 16:30–16:45, IFW B

Vacancy annihilation and ordering kinetics in Ni₂MnAl studied by PALS — •Georg Zagler¹, Pascal Neibecker^1,2, Michael Leitner^1,2, Josef Schmidbauer^1,2, and Christoph Hugenschmidt^1,2 — ¹Physik Department, Technische Universität München, 85747 Garching, Germany — ²Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München, Lichtenbergstr. 1, 85748 Garching, Germany

Heusler alloys are ternary intermetallic compounds with sum formula X₂YZ. These systems are of special interest due to them displaying the ferromagnetic shape memory effect (FSME) with strains larger than those of conventional actuators. While the protoypical ferromagnetic shape memory alloy Ni₂MnGa exhibits a martensitic transition and hence a pronounced FSME, the closely related Ni₂MnAl-System does not show this effect. Presumably this is due to a lack of atomic L2₁ order in the Ni₂MnAl system. Responsible for the reduced degree of order are the slow ordering kinetics in the temperature region of interest. Indirect measurements show that the achievable state of order in this system can however be influenced by quenched-in vacancies. A direct method to study vacancy concentrations in solids is positron annihilation lifetime spectroscopy (PALS). In the outlined work, we investigate the effect of quenched-in vacancies on the ordering kinetics of an off-stoichiometric Ni₂MnAl-alloy by means of PALS. We show a clear reduction of the average positron lifetime with the annealing time in isothermal annealing studies and correlate vacancy concentrations to ordering kinetics as determined by calorimetric measurements.