Talk given by

Prof. Laszlo S. Toth

Lorraine University

Metz, France

Abstract:

Severe plastic deformation (SPD) processes lead to specific microstructures in terms of grain shape and next-neighbor disorientation distributions. Indeed, grain fragmentation - which is the main effect of SPD on crystalline materials - makes the grains less elongated. They become eventually nearly equiaxed at extreme large strains, in the steady state. The modeling of such microstructure evolution requires a polycrystal model that includes grain refinement. Such a modeling was introduced by Toth et al. [1] which is based on the lattice curvature induced grain-rotation. This model has proven to be very successful in reproducing grain sizes, disorientation distributions and texture evolution in several applications [1-9]. Therefore, it is proved now that texture evolution is responsible for the grain fragmentation during SPD (among other effects, like twinning or shear banding).During this lecture first the grain fragmentation model will be presented. Then, in the second part, the modeling efforts that do not take directly into account the grain fragmentation will be discussed, using the self-consistent viscoplastic model [10-14]. Two effects will be discussed: 1. It will be shown that when grain size is very small, partial slip becomes relevant. 2. By reducing the grain size, the polycrystal behavior is approaching the uniform deformation (Taylor-mode); for nano-polycrystals, it is actually the Taylor mode.

References:

1. L.S. Toth, Y. Estrin, R. Lapovok, C.F. Gu, A model of grain fragmentation based on lattice curvature, Acta Materialia, 58 (2010) 1782-1794.

2. A. H. Kobaissy, G. Ayoub, L. S. Toth, S. Mustapha, M. Shehadeh, Continuum Dislocation Dynamics-Based Grain Fragmentation Modeling, International Journal of Plasticity, in press.

3. L.S. Toth, C.F. Gu, Modeling of disorientation axis distribution in severely deformed copper, Scripta Materialia, 69 (2013) 183–186.

4. C.F. Gu, L.S. Toth, B. Beausir, Modeling of large strain hardening during grain refinement, Scripta Materialia, 66 (2012) 250-253.

5. C.F. Gu, L.S. Toth, Texture development and grain refinement in non-equal channel angular pressed Al, Scripta Materialia 67 (2012) 33–36.

6. C.F. Gu, L.S. Toth, M. Arzaghi, C.H.J. Davies, Effect of Strain Path on Grain Refinement in Severely Plastically Deformed Copper, Scripta Materialia, 64 (2011) 284–287.

7. C.F. Gu, L.S. Toth, C.H.J. Davies, Effect of Strain Reversal on Texture and Grain Refinement in Route C Equal Channel Angular Pressing of Copper, Scripta Materialia, 65 (2011), 167-170.

8. C.F. Gu, L.S. Toth, R. Lapovok, C.H.J. Davies, Texture evolution and grain refinement of ultrafine-grained copper during micro-extrusion, Philosophical Magazine, 91 (2011) 273- 290.

9. C.F. Gu and L.S. Toth, The origin of strain reversal texture in equal channel angular pressing, Acta Materialia, 59 (2011) 5749-5757.

10. Werner Skrotzki, Andy Eschke, Bertalan Jonas, Tamas Ungar, Laszlo S. Toth; Yulia Ivanisenko; Lydia Kurmanaeva, New experimental insight into the mechanisms of nanoplasticity, Acta Materialia, 61 (2013) 7271–7284.

11. Li Li, Tamas Ungar, Laszlo S. Toth, Werner Skrotzki, Yan D Wang, Yang Ren, Hahn Choo, Zsolt Fogarassy, Xing T Zhou, Peter K Liaw, Shear-Coupled Grain Growth and Texture Development in a Nanocrystalline Ni-Fe Alloy during Cold Rolling, Metallurgical Transactions, 47 (2016) 6632-6644.

12. C. F. Gu, M. Hoffman, L.S. Toth, Y.D. Zhang, Grain size dependent texture evolution in severely rolled pure copper, Materials Characterization, 101 (2015) 180–188.

13. C.F. Gu, L.S. Toth, Y.D. Zhang, M. Hoffman, Unexpected brass-type texture in rolling of ultrafine-grained copper, Scripta Materialia, 92 (2014) 51-54.

14. L.S. Toth, C.F. Gu, B. Beausir, J.J. Fundenberger, M. Hoffman, Geometrically necessary dislocations favor the Taylor uniform deformation mode in ultra-fine-grained polycrystals, Acta Materialia, 117 (2016) 35-42.

Short presentation:

Prof. Toth is an internationally known personality of the mechanics and materials scientific community since about 1990. He earned his high recognition through his broad knowledge in both mechanics and materials which permits him to make the bridge between these two disciplines. His high standard interdisciplinary activity made him an ideal collaborator in the best laboratories of several countries where he spent long periods. Established now in France, his original scientific activity attracts many excellent foreign scientists for joint research. The recent expertise of Prof. Toth is in the field of experiments and mechanical modeling of textures and microstructures of SPD materials, especially on quantitative modeling of grain refinement. Prof. Toth published 170 refereed papers, his h factor is 41. He founded two laboratories, the laboratory ‘LEM3’ in 2010 counting 160 persons, then the Laboratory of Excellence on Design of Alloy Metals for low-mAss Structures ('DAMAS') in 2012 of which he is currently the director.