Journal of Materials Processing Technology 173 (2006) 53–60 Candidature of equal channel angular pressing for processing of tubular commercial purity-titanium A.V. Nagasekhar, Uday Chakkingal ∗ , P. Venugopal Metal Forming Laboratory, Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036, India Received 16 July 2003; accepted 28 October 2005 Abstract The equal channel angular pressing (ECAP) process is a promising technique for imparting a large plastic deformation to materials without a resultant decrease in cross sectional area. In the present study, the suitability of this technique for the processing of tubular specimens has been investigated. Commercially pure titanium was selected for the study. Tubular specimens were extruded to three passes using two processing routes through an ECAP die with an angle of 150 ◦ between the two intersecting channels. Sand was used as a mandrel during the pressing. Analysis of force–stroke diagram was carried out, work from registered force–stroke diagram was calculated and compared with theoretical calculations. The mechanical properties and the microstructure were also investigated. To determine the influence of surface area to volume ratio of the specimens (referred to as the shape difficulty factor, SDF), data obtained in the current study on ECAP of tubular CP-Titanium was compared with data available in the literature on Hooker extrusion and conventional solid extrusion of CP-Titanium. Improvement in mechanical properties was observed in both the Routes. The grain size was reduced from ∼18 m to ∼12 m. These investigations demonstrate that ECAP is a promising technique for improving properties of tubular materials while ensuring retention of shape (with the possibility of imparting further deformation to the specimen using the same die) and with low pressing pressures. © 2005 Elsevier B.V. All rights reserved. Keywords: Equal channel angular pressing; Severe plastic deformation 1. Introduction Plastic deformation is an effective method of structure alter- ation and properties improvement of different materials. Among the recently developed severe plastic deformation techniques, equal channel angular pressing (ECAP) is a novel deformation process capable of introducing large amount of plastic strain to bulk material by application of uniform simple shear [1].A schematic diagram of ECAP die with sharp and round corner intersections is shown in Fig. 1. The die used for ECAP consists of two channels of equal cross-section that meet at an angle of 2φ. A well-lubricated billet of almost same cross section is placed in the top channel and extruded into the intersecting channel by a punch [2,3]. The main advantage of the ECAP process is that materials can be deformed to very high strains without any decrease in cross-sectional area. ECAP process has the ability to obtain ∗ Corresponding author. Tel.: +91 44 2257 4775; fax: +91 44 2257 4752. E-mail address: udaychak@iitm.ac.in (U. Chakkingal). ultrafine-grained material with submicron or nanometer sized grains with enhanced mechanical properties [4–11]. Most of the published research has dealt with fundamental issues in mate- rials science such as development of subgrain structures, grain refinement, formation of shear bands and development of tex- ture in solid materials. Work related to property enhancement of tubular specimens using ECAP has not been reported. The aim of the present work is to study the candidature of the ECAP process for processing of materials in tubular form. Com- mercially pure titanium (CP-Titanium) was used for the study. Force–stroke data were recorded during pressing and compared with theoretical analysis. The scientific parameter that charac- terizes the resistance to flow during extrusion is the surface area/volume ratio of the specimens (here after referred to as the shape difficulty factor, SDF). As the shape difficulty factor is high in tubular specimen geometries compared to solid shapes, significant differences are expected as far as extrusion/pressing pressures, microstructures, and mechanical properties are con- cerned. In general, higher the value of SDF, higher is the pressure needed for extrusion. In extrusion of tubes, an addition to the extrusion pressure arises due to the presence of the mandrel. 0924-0136/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2005.10.024