Back to overview

Lecture

WEB High-Cycle Fatigue Behavior of Single Crystalline Ni-Mn-Ga Magnetic Shape Memory Alloys

Wednesday (27.05.2020)
16:50 - 17:10 Room 1
Part of:


Magnetic Shape Memory (MSM) alloys are a class of smart materials exhibiting the ability to change size and shape when subjected to a magnetic field or an external stress, generating, thus, force and motion [1,2]. The effect is based on the reorientation of twin variants in the martensitic phase [3]. MSM alloys are promising candidates for application in actuators, sensors, dampers, and energy harvesting devices due to their outstanding properties. These applications demand materials with minimal fatigue effects during millions of actuation cycles.

 

The present study focuses on the changes in microstructure of single crystalline off-stoichiometric Ni2MnGa samples exhibiting a five-layered (10M) superstructure and up to 7% strain during high-cycle actuation in a custom-built testing device.

 

The magneto-mechanical properties indicate a decrease of strain, twinning stress, and work output density during actuation cycling of up to 100 million times. The development of cracks corresponding roughly to the {111} crystal planes is found to be associated, among others, with the presence of impurities or inclusions in the material. Crack growth occurs mostly along the low angle boundaries with varying tilt. The twinning microstructure after fatigue can be characterized by pinned twin variants and branching behavior of twins due to the formation of persistent slip bands containing both edge and screw dislocations pinning the mobile twin boundaries. The fracture plane is perpendicular to the {101} twin planes and follows the ladder structure of the persistent slip bands comprised of edge dislocations. Steps in the fracture plane correspond to changes in the modulation direction.

 

[1] R. Chulist, E. Pagounis, A. Böhm, C.G. Oertel, W. Skrotzki, Scripta Mater., 67 (2012), 364.

[2] E. Pagounis, M.J. Szczerba, R. Chulist, M. Laufenberg, Scripta Mater., 83 (2014), 29.

[3] Y. Ge, O. Heczko, O. Söderberg, and S.P. Hannula, Appl. Phys. Lett., 89 (2006), 082502.

Speaker:
Jonas Heider
ETO MAGNETIC GmbH
Additional Authors:
  • Dr. Emmanouel Pagounis
    ETO MAGNETIC GmbH
  • Dr. Markus Laufenberg
    ETO MAGNETIC GmbH