Influence of stacking-fault energy on the accommodation of severe shear strain in Cu-Al alloys during equal-channel angu
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Gang Yang Central Iron and Steel Research Institute, Beijing 100081, China
Shiding Wua) and Zhe-Feng Zhangb) Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China (Received 27 March 2009; accepted 29 June 2009)
X-ray diffraction (XRD) and transmission electron microscope (TEM) investigations have been carried out to decode the influence of stacking-fault energy (SFE) on the accommodation of large shear deformation in Cu-Al alloys subjected to one-pass equal-channel angular pressing. XRD results exhibit that the microstrain and density of dislocations initially increased with the reduction in the SFE, whereas they sharply decreased with a further decrease in SFE. By systematic TEM observations, we noticed that the accommodation mechanism of intense shear strain was gradually transformed from dislocation slip to deformation twin when SFE was lowered. Meanwhile, twin intersections and internal twins were also observed in the Cu-Al alloy with extremely low SFE. Due to the large external plastic deformation, microscale shear bands, as an inherent deformation mechanism, are increasingly significant to help carry the high local plasticity because low SFE facilitates the formation of shear bands.
I. INTRODUCTION
During the last two decades, bulk ultrafine grained (UFG) or nanocrystalline (NC) materials have been investigated extensively due to their new physical and enhanced mechanical properties.1–3 Various approaches based on severe plastic deformation (SPD)-induced grain refinement have been developed for synthesizing UFG/NC materials, including equal-channel angular pressing (ECAP),4–14 highpressure torsion (HPT),15–17 accumulative roll bonding (ARB),18 low temperature rolling (LTR),19 and dynamic plastic deformation (DPD).20–22 Among them, ECAP is considered as one of the most important and efficient SPD methods to produce bulk UFG materials while maintaining their original geometry.2 As one of the major SPD methods, ECAP has been used to experimentally explore many materials with different crystallographic structures (fcc, bcc, and hcp), such as Al, Cu, Fe, and Ti.4,6,9,23,24 A comprehensive understanding of grain-refinement mechanisms in these materials has been achieved by taking into account dislocation activity, deformation twinning, and phase Address all correspondence to these authors: a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2009.0426 3636
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J. Mater. Res., Vol. 24, No. 12, Dec 2009 Downloaded: 13 Mar 2015
transformation.1,10,11,13 However, the influence of stacking-fault energy (SFE), one of the most important parameters in cubic structured materials, on the grain refinement and strain accommodation during ECAP is much less understood.9,11,13 In close-packed structures, SFE determines the extent of dislocation dissociation, affecting not only the dislocation substructures but also deformation behavior of the materials.25–27 It has been well known that the higher th
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