Deformation via the Transformation of Hierarchical Microstructures
Final Report Abstract
The technological relevance of magnetic shape-memory alloys (MSMA) is due to the coupling of functional and structural properties. The exceptional functional abilities are the magnetic-fieldinduced-strain (MFIS) and the strain-induced change of magnetization, both of which can be used - for instance - in microelectromechanical systems. The ability and extend of MFIS depends strongly on the twin microstructure of MSMA single crystals. MSMA microstructures generally hierarchical: twinned domains exist within twinned domains. As such, three hierarchical levels can be observed from the nanometer to the millimeter-scale. It should be noted that the microstructure changes substantially during magnetic loading: twins grow, rearrange and shrink. Additional complexity is introduced by the atomistic structure: while 14-layered modulated martensitic structures have an exceptionally large MFIS; non-modulated martensitic structures have generally no MFIS. Concluding, the microstructure plays an important role in determining the functional properties of MSMA. The project established a quantitative microstructure - property relationships of twin-structures and understanding the differences between macroscopic and microscopic twinning stresses. Although applied to the specific MSMA, we investigated fundamentally microstructural effects on twinning, which occurs in all shape-memory alloys. We developed a discrete disclination dynamics model that is based on previous higher-scale dislocation studies. The disclination simulation tool is capable to evaluate microstructure evolution on multiple hierarchical length-scales and hence allow understanding the microstructure - property relationships of MSMAs. The project was funded by the National Science Foundation (USA) and the German Research Foundation and the work is a collaboration of: Peter Müllner, Brittany Muntifering and Bill Knowlton: Boise State University, USA; Steffen Brinckmann, Benjamin Reinholz: Max-Planck Insitut für Eisenforschung, Germany; Alexander Hartmaier: ICAMS, Ruhr-Universität Bochum, Germany.
Publications
- Application of Disclination Dynamics: Twin boundary motion in magnetic shape-memory alloys, 4th Int. Conf. Ferromagnetic Shape Memory Alloys, Boise, 06/2013
B. Reinholz, S. Brinckmann, A. Hartmaier, B. Muntifering, W. Knowlton, P. Müllner
- Discrete Disclination Dynamics & Discrete Dislocation Dynamics, 4th Int. Conf. Ferromagnetic Shape Memory Alloys, Boise, 06/2013
S. Brinckmann, B. Reinholz, A. Hartmaier, B. Muntifering, W.B. Knowlton, P. Müllner
- Discrete Disclination Dynamics in comparison to Discrete Dislocation Dynamics, SES 50 th Annual Technical Meeting, Providence, 07/2013
S. Brinckmann, B. Reinholz, A. Hartmaier, B. Muntifering, P. Müllner
