Deformation behavior of copper during a high pressure torsion process
Introduction
Recently, several methods of severe plastic deformation were developed to process bulk nanostructured materials with a grain size from 20 to 200 nm depending on a number of factors [1]. The high pressure torsion (HPT) process has been subject of many investigations as a new method of processing bulk nanostructured materials. By this method nanostructures can be formed both by the consolidation of nanopowders [2] and the refinement of the coarse-grained microstructures [3]. The presence of high angle grain boundaries [4] and high intrinsic stresses are the main features of the obtained nanostructured materials [1].
Fig. 1 shows a schematic representation of the HPT process. A workpiece is held between anvils (upper ram and lower support) and strained in compression under the applied pressure of several GPa. After pressing and holding the workpiece using the upper holder, the lower holder rotates and surface friction forces between the workpiece and the rotating lower die deform the workpiece by shear force.
Because the mechanical properties of the deformed material are directly related to the amount of plastic deformation, i.e. the developed strain, understanding the phenomenon associated with strain development is very important in severe plastic deformation processes. The knowledge of absolute values and the homogeneity of internal stress and strain distributions is still very desirable in order to optimize the processes of grain size refinement and nanostructure development at the HPT process.
In this study, the results of the elasto-plastic finite element analysis of the elasto-plastic deformation behavior of bulk materials during the HPT processing are presented. The simulated geometry of the workpiece is compared with the experimental data of pure copper samples processed by the HPT process.
Section snippets
Experimental procedures
Pure Cu (99.9%) samples annealed at 600 °C for 10 h and having an initial disk shape with a diameter of 10 mm and a height of 0.7 mm were used as ingots for the following deformation in a special device. In this device the ingots were put between two flat heads under a high imposed pressure of about 5 GPa. The lower head was rotated with at rate of 0.012 rad s−1. The friction forces between the heads and the ingot result in the shear deformation of the workpiece.
One ingot was subjected to pure
Finite element analysis
The isothermal finite element simulations of the HPT process have been carried out using the commercial elasto-plastic finite element code, ABAQUS [5]. In the simulations, the initial dimension of the workpiece was 10 mm in diameter and 0.7 mm in thickness. The radius of the die was 10 mm, which is the same as that of the workpiece.
Fig. 2 shows the initial finite element mesh system for the plastic deformation analysis during the HPT process. A quarter of the workpiece was selected as the
Results and discussion
Fig. 4 shows the deformed geometry of a copper sample after the HPT processes of (a) compressed state with 5 GPa, (b) unloaded state after compression (5 GPa), and (c) compression (5 GPa)–die rotation (36°)–unloaded state. The outer part of the workpiece out of the die was thickened. Although, the geometry of the deformed workpiece is not distinguishable in Fig. 4(a) and (b), it can be shown that the thickness of the unloaded workpiece is not uniform because of an elastic recovery, see Fig. 5. The
Summary
In this study, the results of the elasto-plastic finite element analysis of pure copper during the HPT process using the von-Mises model was presented. The deformation geometry of the workpiece was investigated. The thickness of the workpiece decreased with distance from the center because of the higher compressive plastic stress in the center compared to the outer part during the loading state and the elastic recovery during unloading. The circumferential displacement decreases with the
Acknowledgements
This research was supported by a grant from the Center for Advanced Materials Processing (CAMP) of the 21st Century Frontier R&D Program funded by the Ministry of Science and Technology, Korea.
References (8)
- et al.
Structure and properties of ultrafine-grained materials
Mater. Sci. Eng. A
(1993) Finite element analysis of torsional deformation
Mater. Sci. Eng. A
(2001)Developing SPD methods for processing bulk nanostructured materials with enhanced properties
Met. Mater. Int.
(2001)- et al.
Microstructures and properties of nanocomposites obtained through SPTS consolidation of powders
Metall. Mater. Trans. A
(1998)
Cited by (60)
Large elastoplastic deformation of a sample under compression and torsion in a rotational diamond anvil cell under megabar pressures
2017, International Journal of PlasticityCitation Excerpt :There are some recent studies on modeling and simulation of plastic flow (Levitas and Zarechnyy, 2010b) and strain-induced PTs in a RDAC (Feng and Levitas, 2013, 2016; Feng et al., 2014; Levitas and Zarechnyy, 2010a), where assumptions of small elastic strains in the sample, pressure-independent yield strength, and rigid diamond were utilized. There are also FEM simulations of HPT (e.g (Beygelzimer et al., 2016; Edalati et al., 2016; Figueiredo et al., 2011; Kim, 2001; Kim et al., 2003; Yoon et al., 2008)) for rigid-plastic materials and pressure-independent yield strength. These assumptions make the models unsuitable for processes in a RDAC under megabar pressures.
Mechanical alloying via high-pressure torsion of the immiscible Cu<inf>50</inf>Ta<inf>50</inf> system
2017, Materials Science and Engineering: AAn examination of the elastic distortions of anvils in high-pressure torsion
2015, Materials Science and Engineering: A