1. High Pressure Torsion Extrusion: A Scale-Up of HPT

In collaboration with Brigitte Baretzky (INT) we scaled up the HPT method for the processing of advanced nanocrystalline materials in amounts reasonable for industrial applications. The new method is named High Pressure Torsion Extrusion (HPTE). During HPTE, a rod-shape specimen is extruded through sectional containers rotating relative to each other (Fig. 2). The specimen is subjected to shear deformation in the area where the containers meet. One of the main advantages of the HPTE process is that already after a single extrusion pass a high accumulated strain (orders of magnitude lager than for Equal Channel Angular Pressing, Twist Extrusion, Cyclic Extrusion Compression, etc.) can be achieved in the specimen. At present, commercially pure copper and electro-technical Al alloy 6101 were successfully processed using HPTE. As a result uniform UFG microstructure was formed and high mechanical properties were achieved.

Furthermore, the presence of a strong velocity gradient in the specimen cross-section during HPTE provides the possibility to process hybrid materials or composite parts with helical architecture of functional elements. Simulations predict that such composites can combine high strength and ductility. This approach is being studied now in the frames of a German Research Society (Deutsche Forschungsgemeinschaft, DFG) Project „Hybrid ultrafine grained materials produced by high pressure torsion extrusion” (IV98/8-1, 2017-2020).

Publications

• Device and method for forming components made of metallic materials V. Fedorov, Yu. Ivanisenko, B. Baretzky, and H. Hahn, European patent EP 2 821 156 B1

• High Pressure Torsion Extrusion as a new severe plastic deformation process Yu. Ivanisenko, R. Kulagin, V. Fedorov, A. Mazilkin, T. Scherer, B. Baretzky, and H. Hahn Mat. Sci. Eng. 2016, A664: 247-256, DOI: 10.1016/j.msea.2016.04.008

2. Mechanical behaviour of nanoglasses

In collaboration with R. Schwaiger Group we analyzed the mechanical performance of Cu₅₀Zr₅₀ metallic nanoglasses. We found that the hardness and Young's modulus increase for the nanoglasses compared to melt-spun ribbons. The curves of both as prepared and annealed nanoglass samples are smooth without any pop-ins (indicating homogeneous deformation), while the load vs displacement curves of the melt-spun ribbon of similar composition show clear pop-ins (serrations), indicating the generation of shear bands (inhomogeneous deformation) (Fig. 3a). The area in the vicinity of the Vickers indents in nanoglass (Fig. 3b) clearly does not show any shear bands around the indent whereas the melt-spun ribbons shows shear bands around the indent. It is proposed that the interfacial regions, which are sources of high free volume act as nucleating sites for the formation of numerous shear transformation zones giving rise to homogeneous deformation in nanoglasses.

Publications

• Cu-Zr nanoglasses: atomic structure, thermal stability and indentation properties S.H. Nandam, Yu. Ivanisenko, R. Schwaiger, Z. Śniadecki, X. Mu, D. Wang, R. Chellali, T. Boll, A. Kilmametov, T. Bergfeldt, H. Gleiter, and H. Hahn, Acta Materialia 2017, 136, 181-189. DOI: 10.1016/j.actamat.2017.07.001

3. Mechanically driven phase transformations

Being applied to alloys, severe plastic deformation often leads to mechanically driven phase transformations like forced mixing in immiscible alloy systems, decomposition of supersaturated solid solutions, dissolution of second phase particles or even amorphization.  In our group we study mechanically driven cementite dissolution in pearlitic steels, mixing in immiscible Cu-Ag or Cu-Nb systems and the formation of high pressure w phase in Ti and Ti alloys. Our aim is to understand the physical mechanisms of these processes.

Publications

• Forced chemical mixing of immiscible Ag-Cu heterointerfaces using high-pressure torsion M. Pouryazdan, D. Schwen, D. Wang, T. Scherer, H. Hahn, R. S. Averback, and P. Bellon, Phys. Rev. B 2012, 86, 144302. DOI: 10.1103/PhysRevB.86.144302

• Transformations of Cu in supersaturated solid solutions under high-pressure torsion B.B. Straumal, A.R. Kilmametov, A.A. Mazilkin, L. Kurmanaeva, Y. Ivanisenko, A. Korneva, P. Zięba, and B. Baretzky, Matt Lett. 2015, 138, 255–258, DOI: 10.1016/j.matlet.2014.10.009

• Phase Transformations in Ti–Fe Alloys Induced by High-Pressure Torsion B.B. Straumal, A.R. Kilmametov, Yu. Ivanisenko, A.S. Gornakova, A.A. Mazilkin, M.J. Kriegel, O.B. Fabrichnaya, B. Baretzky and H. Hahn, Adv. Eng. Mat. 2015, 17, 1835–1841, DOI: 10.1002/adem.201500143

• Self-organized, size-selection of precipitates during severe plastic deformation of dilute Cu-Nb alloys at low temperatures  J.A. Beach, M. Wang, P. Bellon, S. Dillon, Yu. Ivanisenko, T. Boll, and R.S. Averback, Acta Mater. 2017, 140, 217-223 DOI:10.1016/j.actamat.2017.08.041

• The α→ω and β→ω phase transformations in Ti–Fe alloys under high-pressure torsion A.R. Kilmametov, Yu. Ivanisenko, A.A. Mazilkin, B.B. Straumal, A.S. Gornakova, O.B. Fabrichnaya, M.J. Kriegel, D. Rafaja, and H. Hahn, Acta Mater. 2017, 144, 337-351, DOI: 10.1016/j.actamat.2017.10.051

4. Mechanical behavior of nanocrystalline high entropy alloys

This project is aimed to establish the influence of the severe plastic deformation by high pressure torsion on the microstructure, phase composition and the resulting mechanical properties of a high entropy alloys.

Publications

• FCC nanostructured TiFeCoNi alloy with multi-scale grains and enhanced plasticity Z. Fu, B. E. MacDonald, D. Zhang; B. Wu, W. Chen, J. Ivanisenko, H. Hahn, E. J. Lavernia, Scripta materialia 2018, 143, 108–112. DOI: 10.1016/j.scriptamat.2017.09.023

• Evolution of Microstructure and Mechanical Properties of a CoCrFeMnNi High-Entropy Alloy during High-Pressure Torsion at Room and Cryogenic Temperatures S. Zherebtsov, N. Stepanov, Yu. Ivanisenko, D. Shaysultanov, N. Yurchenko, M. Klimova, G. Salishchev, Metals 2018, 8(2), 123,  DOI: 10.3390/met8020123

5. High-strength Al-based alloys with high electric conductivity

Due to the combination of low weight, good electrical conductivity and technological plasticity, as well as high resistance to atmospheric corrosion, aluminum and a number of alloys based on it are widely used in electrical engineering, displacing more expensive copper-based conductor materials. One of the main disadvantages of aluminum conductors is their low strength compared to copper. The proposed project is focused on the development of a new generation of electric conducting materials with properties enhanced thanks to the microstructure design – a purposeful formation of nanostructures with specified parameters. Alloys under investigation will be nanostructured using an invented at INT KIT method of severe plastic deformation by High Pressure Torsion Extrusion, and subsequently artificially aged to additionally benefit from precipitation hardening. The precipitation kinetics, as well as the subtle structure of precipitates and their distribution in the microstructure is studied in collaboration with Prof. Dr. Christan Kübel using high-end electron microscopy. As a result we plan to produce nanostructured wires of the high strength Al alloys with enhanced electric conductivity.

6. Fatigue and corrosion performance of ultrafine-grained Mg-based alloys

This is a new research project, funded by DFG, which we perform in collaboration with Prof. Dr. Eberhard Kerscher from TU Kaiserslautern. The main aim of the project is to study the microstructure and texture evolution in two model biocompatible Mg alloys during different HPTE routes and subsequent thermal treatment, and the effect of the developed microstructure and texture on the monotonic and cyclic mechanical properties, even in corrosive environments. Application of Mg alloys as implant materials is limited due to their low strength, which is often lower than the human bone strength. Furthermore, they demonstrate low corrosion resistance in the presence of strengthening precipitates. In order to improve the performance of chosen alloys, High Pressure Torsion Extrusion will be used which will allow to increase the strength due to (sub)grain boundary strengthening without forming precipitates which might be critical in corrosive environments.