Abstract
The microstructure and mechanical properties of rod-shaped samples (measuring 11.8 mm in diameter and 35 mm in length) of commercially pure (CP) copper were characterized after they were processed by high pressure torsion extrusion (HPTE). During HPTE, CP copper was subjected to extremely high strains, ranging from 5.2 at central area of the sample to 22.4 at its edge. This high but varying strain across the sample section resulted in HPTE copper displaying a gradient structure, consisting of fine grains in the central area and of ultrafine grains both in the middle-radius area and at the sample edge. A detailed analysis of the tensile characteristics showed that the strength of HPTE copper with its gradient structure is similar to that of copper after severe plastic deformation (SPD) techniques, typically displaying a homogeneous structure. Detailed analysis of the contributions of various strengthening mechanisms to the overall strength of HPTE coper revealed the following: The main contribution comes from Hall–Petch strengthening due to the presence of high and low angle grain boundaries in gradient structure, which act as effective obstacles to dislocation motion. Therefore, both types of boundaries should be taken into account in the Hall–Petch equation. This study on CP copper demonstrated the potential of using the HPTE method for producing high-strength metallic materials in bulk form for industrial use.
Highlights
During past three decades, numerous studies have been conducted on the structure and mechanical properties of bulk nanostructured (NS) and ultra-fine-grained (UFG) materials produced by severe plastic deformation (SPD) processing
This study aims to bridge this gap by conducting a critical analysis of both the structure and the mechanical test results obtained on high pressure torsion extrusion (HPTE)-processed Cu rod samples to reveal possible strengthening effects of varying grain refinement steps giving rise to gradient structures
It was shown that HPTE equipment can be used to produce commercially pure (CP) Cu rods combining both high strength and large elongation to failure
Summary
Numerous studies have been conducted on the structure and mechanical properties of bulk nanostructured (NS) and ultra-fine-grained (UFG) materials produced by severe plastic deformation (SPD) processing. In these studies, considerable effort has been devoted to high pressure torsion (HPT) [1,2] as well as equal channel angular pressing (ECAP) [3,4,5] since these two are the best-known SPD techniques for producing UFG metallic materials. UFG materials with unique combinations of mechanical properties such as high strength and plasticity [6] have generated intensive interest because the results of some studies have suggested the presence of new strengthening mechanisms.
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