Complex Metallic Alloys: Plasticity and Defects
Final Report Abstract
During the first funding period we largely focused the work on metadislocations in 8-type phases and the investigation of the macroscopic plastic deformation behaviour of complex metallic alloys (CMAs) of different structure. On this basis we proceeded with the work in the reporting period. As announced in the work plan, we devoted a major body of work to the detailed investigation of dislocation cores by high-resolution (scanning) transmission electron microscopy, taking advantage of the state-of-the-art microscopes available at Jülich. In the reporting period we indeed succeeded to accomplish this goal for three different CMA phases, for orthorhombic Al13Co4, the orthorhombic Taylor phase T-Al-Pd-Mn, and the orthorhombic 86 phase in the system Al-Pd-Mn. For all three phases we imaged metadislocation cores at high resolution and established structure models for the core structures. We could show that the structure of metadislocation cores, as the bulk, is based on clusters, and that the strain is confined to a small localized area. Exceeding the work plan, we employed the core-structure models to build models for metadislocation motion. We could show that the movement of metadislocations by an elementary glide or climb step, which advances the core by about 12 to 24 nm (depending on the structure), involves short jumps of the individual atoms of a few Ångstrom only. This explains why such complex and extended defects as metadislocations can establish a deformation mechanism in an energetically acceptable way. For the simplest of the investigated core structures, that of Al13Co4, by a complementary DFT approach we could extend the model to a full three-dimensional description including all constituting atomic species. Employing a simulated annealing procedure, we could advance this model to a full 3D model of metadislocation motion in Al13Co4. The approach is general and versatile enough to be applied to more complex cases, such as metadislocation movement in 86-Al-Pd-Mn, involving more atoms and motion by climb. The work carried out in the reporting period on metadislocations in structures other than that of orthorhombic 86-Al-Pd-M, in which they were originally discovered, allows for a more general description of metadislocations. We can now comprehensively understand metadislocations as small partial dislocations in a structure of large lattice parameters, which are accommodated in the material by association of a localized area of different but closely related structure. The presence of suitable related phases provides an additional degree of freedom, which decreases the activation energy for local atomic rearrangements, enabling movement of dislocations at a stress level below a critical limit. The generalized understanding of metadislocation also allowed us to develop a model for the description of the elastic energy of metadislocations, which is valid for metadislocations in all CMA phases investigated. On a more macroscopic level, we succeeded to identify a deformation mechanism acting in CMA phases in which the stress is mediated by dislocations moving by pure climb. This mechanism, which we refer to as complementary climb, involves two systems of dislocations: one system consists of dislocations moving by positive climb and acts as vacancy source, the other by negative climb and acts as vacancy sink. Simultaneous activation of both systems of dislocations leads to an exchange of vacancies, thus ensuring continuous mobility at short vacancy-diffusion distances.
Publications
- Metadislocations. Invited chapter in Dislocations in Solids Vol 16 (30th Anniversary Volume dedicated to Frank Nabarro) (Eds. J.P. Hirth and L. Kubin). Elsevier 2009, p.110
M. Feuerbacher and M. Heggen
- Composite Defects in the Complex Metallic Alloy C2-Al-Pd-Fe. Intermetallics 18, 2010, 1560
M. Heggen and M. Feuerbacher
- Metadislocations in Complex Metallic Alloys. In Complex Metallic Alloys- Vol 4: Mechanical Properties (Ed. E. Belin-Ferre) World Scientific, Singapore 2010
M. Heggen and M. Feuerbacher
- On the mechanical and tribological behavior of Al3Mg2 complex metallic alloys as bulk material or as sputtered coating. Intermetallics 18, 2010, 2096
S. Achanta, M. Feuerbacher, A. Grishin, X. Ye, J.-P.Celis
- Plastic deformation mechanism in complex solids. Nature Materials 9, 2010, 332
M. Heggen, L. Houben, M. Feuerbacher
- Plastic deformation properties of the complex metallic alloy phase μ-Al-Mn. Intermetallics 18, 2010, 1737
S. Roitsch, M. Heggen, M. Feuerbacher
- The Plasticity of Metals: Basic Concepts. In Complex Metallic Alloys- Vol 4: Mechanical Properties (Ed. E. Belin-Ferre) World Scientific, Singapore 2010
M. Feuerbacher
- Metadislocations in Complex Metallic Alloys and their Relation to Dislocations in Icosahedral Quasicrystals. Israel Journal of Chemistry, 51, 2011, 1235
M. Feuerbacher and M. Heggen
- Metadislocations in the complex metallic alloys T-Al-Mn-(Pd, Fe). Acta Mater. 59, 2011, 4458
M. Heggen, L. Houben, M. Feuerbacher
- Novel Defects in Al-Pd-Fe Complex Metallic Alloys: A Micromechanical Modelling Approach. Intermetallics 19, 2011, 99
K.V. Mani Krishna, A. Arya, M. Heggen, G. K. Dey, M. Feuerbacher, S. Banerjee
- Dislocations in Icosahedral Quasicrystals. Invited Review. Chem. Soc. Rev. 41, 2012, 6745
M. Feuerbacher
- Elastic Energy of Metadislocations in Complex Metallic Alloys. Acta Mat. 60, 2012, 1703
M. Feuerbacher and M. Heggen
- Metadislocation core structure and atomic model for metadislocation motion. Acta Mat. 61, 2013, 3851
M. Heggen and M. Feuerbacher
(See online at https://doi.org/10.1016/j.actamat.2013.03.023) - Core structure and motion of metadislocations in the orthorhombic structurally complex alloy Al13Co4. Mat. Res. Lett., 2014
M. Heggen and M. Feuerbacher
(See online at https://doi.org/10.1080/21663831.2014.882869) - On the stability of metadislocations with 16 associated phason planes. Intermetallics 53, 2014, 187
M. Heidelmann, M. Heggen, and M. Feuerbacher
(See online at https://doi.org/10.1016/j.intermet.2014.05.005) - Comprehensive model of metadislocation movement in Al13Co4. Scripta Mat. 98, 2015, 24
M. Heidelmann, M. Heggen, C. Dwyer, and M. Feuerbacher
(See online at https://doi.org/10.1016/j.scriptamat.2014.11.006)
