Microstructural evolution of equal channel angular drawn purity titanium at room temperature Hong Zhao, Yuping Ren ** , Bo Yang, Gaowu Qin * Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials Science and Engineering, Northeastern University, Shenyang, 110819, China article info Article history: Received 5 June 2019 Received in revised form 29 July 2019 Accepted 24 August 2019 Available online 26 August 2019 Keywords: ECAD Microbands FCC phase Small size Drawing speed abstract Thin commercial-purity titanium (CPeTi) wire was successfully acquired by equal channel angular drawing (ECAD) at room temperature with route Bc using a 90  die at a relatively high drawing speed of 10 mm s 1 . The as-drawn CPeTi wires were of good quality free of cracks and segmentation on their surface. The grain size of CPeTi was reduced from ~32 mm for the as-annealed wire to ~700 nm for 12- passes equal channel angular drawn wire. The grain experienced transition from microband to thin lath and to equiaxed subgrains with the increment in drawing passes. Face-centered cubic (FCC) phase was triggered obviously to accommodate the large shear strain induced by ECAD at the drawing rate of 20 mms 1 . The thickness of the FCC phase increased with an increase in drawing passes, and no equiaxed subgrains were formed in CPeTi. Accordingly, the drawing speed significantly affects the deformation mode and microstructural evolution of CPeTi during ECAD. A lower drawing speed provides a longer time for the structure recovery, thus resulting in the occurrence of dynamic recovery when ECAD was performed at room temperature. Additionally, f10 12g tension twinning and f11 22g compression twinning occurred simultaneously to accommodate ECAD shear deformation. The success in processing CPeTi rods at room temperature through multiple passes of ECAD provides a new perspective to effi- ciently fabricate ultrafine grained small-sized materials continuously. © 2019 Elsevier B.V. All rights reserved. 1. Introduction As one of the most typical severe plastic deformation (SPD) techniques [1], equal channel angular pressing (ECAP) is an efficient process to produce titanium with ultrafine grains. Consequently, improved mechanical properties of CPeTi are comparable to those of Ti-6Al-4V alloy and suitable for use as biomedical devices, such as bone pins and dental implants [2e5]. The exploitation of CPeTi is in coincidence with for the concept of compositional plainification and sustainability improvement [6]. In general, the processing of CPeTi by ECAP is conducted at elevated temperatures (473e873 K) [7e12] with a relatively slow ram speed of 0.25e8 mm s 1 [7 , 12e15]. The grain size of CPeTi can be refined to 100e700 nm after four to eight passes of ECAP. However, CPeTi processed by ECAP at room temperature was inclined to split when it was pressed at a speed higher than 10 mm s 1 despite using specially designed die and composite lubricant [16e20]. Apart from restrictions in temperature and ram speed, the di- mensions of billets for ECAP were confined to be no less than 10 mm in diameter and no more than 150mm in length. Whereas with regard to biomaterials, the diameter of most bone pins and dental implants is below 2 mm and even is as small as 0.5 mm [21 ,22]. Therefore, medical pure titanium rod with ultrafine grains is difficult to be obtained directly by ECAP. Chakkingal et al. [23,24] found that the coarse grain size of 2000 mm could be reduced significantly to 1 mm by conducting six passes of ECAD on cast aluminum bars at room temperature. In comparison with ECAP, ECAD is a more innovative technique to draw samples through intersecting channels [23,24] and is more feasible to continuously process longer wires with smaller diameter. Therefore, ECAD will become a new processing method to produce ultrafine-grained metal wires. We aim to apply ECAD technology to process CPeTi rods and investigate the effect of high drawing speed on microstructural evolutions. This research provides a new approach to efficiently fabricate small-sized CPeTi with ultrafine grains continuously at room temperature. * Corresponding author. ** Corresponding author. E-mail address: qingw@smm.neu.edu.cn (G. Qin). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom https://doi.org/10.1016/j.jallcom.2019.152002 0925-8388/© 2019 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds 811 (2019) 152002