Elsevier

Journal of Alloys and Compounds

Volume 578, 25 November 2013, Pages 369-372
Journal of Alloys and Compounds

Letter
Microstructure and texture evolutions and mechanical properties in pure copper by equal-channel angular pressing

https://doi.org/10.1016/j.jallcom.2013.06.024Get rights and content

Abstract

Pure copper (99.99%) rod is subjected to equal-channel angular pressing (ECAP) at room temperature through a die with 90° between the die channels. After one pressing, the mean grain size had a sharp decrease from the initial 36.71 μm to 13.23 μm and ideal components of simple shear textures were developed. Inhomogeneous microstructures are aligned with the shearing direction and the sub-boundary structure is elongated in the shear direction and a large amount of dislocation tangles are formed inside sub-grains. The {1 1 1}〈1 1 0〉 slip mode is found to be the main deformation mode during ECAP and mechanical properties were also examined by tensile tests at room temperature.

Introduction

Severe plastic deformation (SPD) has been arousing great scientific interest, especially due to its capacity of producing materials which display unusual properties, such as equal-channel angular pressing (ECAP) [1], [2], [3], [4], [5], high pressure torsion (HPT) [6], and dynamic plastic deformation (DPD) [7]. Among these methods, ECAP is an especially attractive processing technique for its simple procedure to produce bulk, fully dense, ultra-fine grained (UFG) materials in relatively short processing time [8], [9], [10], [11]. Another noticeable observation in the stress–strain curves of UFG materials is that very little work hardening, which in turn is due to the high defect density in the ECAP materials. In a first pass, the equal-channel angular extrusion (ECAE) process can impart substantial microstructure and texture evolution to a material [12], [13], [14]. These alternations in the subgrain microstructure and texture could contribute to accommodate the severe plastic strains and rotations during ECAP process. Qu et al. have reported that the grain refinement mechanism was gradually transformed from dislocation subdivision to twin fragmentation by tailoring the SFE of Cu alloys [15]. Sun et al. have proposed that grain subdivision and texture evolution, as well as local boundary migration, were possible mechanisms involved in the formation of submicron grains in aluminum [16]. Al-Maharbi et al. have shown that initial textures and ECAP route effects on the active deformation modes which were responsible for specific grain size and distribution, and grain morphology in AZ31B magnesium alloy [17]. In general, grain refinement and texture evolution have been investigated separately and few systematic investigations have been performed on the concomitant development of texture and microstructure.

In this study, a copper rod was pressed at an inner angle Φ = 90° and the process was interrupted half way during the first pass of the ECAP process. The intensive EBSD analyses on an un-deformed area and the completely ECAPed area were conducted to capture the formation of the microstructure and texture in order to understand dominating deformation mechanisms. Transmission electron microscopy (TEM) was used to investigate more detailed information about the microstructures after one passed specimen. Mechanical properties of the initial and one passed specimens were investigated by tensile testing.

Section snippets

Experimental procedures

A commercially available copper rod (Ø12 mm × 80 mm) was used which was annealed at 500 °C for 1 h before processing via ECAE. In the ECAP process, the specimen was coated with a lubricant containing MoS2, with a ram speed of 1 mm/s and without any back-pressure. A single pass was interrupted, leaving one-half of the rods as in the initial states and the rest in the one-pass states. Using wire electrical discharge machining (EDM), 2 mm thin plate was cut from the mid-plane of the interrupted specimen.

Results and discussion

Fig. 1b and c show typical EBSD maps obtained from the center portion of the specimen before (position 1 in Fig. 1a) and after subjection to one pass (position 2 in Fig. 1a) on the section ID-ED plane. In recent studies [18], the texture heterogeneity was investigated through the thickness (along ID) of a pure Cu material deformed by first ECAP pass with a Φ = 90° die. In this study, center region was measured and analyzed. The initial Cu has large nearly equiaxed grains and often twinned has

Conclusions

The evolutions of microstructure and texture for a one pass heavily deformed submicron grain copper have been characterized by using EBSD and TEM analyses. The following conclusions can be drawn:

  • 1.

    The equiaxed grains developed into elongated (lamellar) low angle boundary grains and average grain size was decreased dramatically only after the one pass.

  • 2.

    {1 1 1}〈1 1 0〉 slip mode was mainly activated and large amount of dislocation tangles are formed inside sub-grains during ECAP process.

  • 3.

    The texture

Acknowledgement

Nguyen Dang Nam is grateful for the support of Alfred Deakin Postdoctoral Research Fellowship Scheme (ADPRF 2012).

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