Modeling of the ECAP Induced Strain Hardening Behavior in FCC Metals
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INTRODUCTION
ULTRAFINE-GRAINED microstructure in metallic materials is manufactured by using severe plastic deformation methods, which consecutively result in mechanical properties alteration. The most common severe plastic deformation and grain refinement techniques are equal channel angular pressing (ECAP), high-pressure torsion, and accumulated roll bonding.[1] ECAP is an effective method that was first introduced by Segal in the 1970s[2] and is used to enhance the mechanical properties by achieving exceptional grain refinement.[3–5] ECAP is a metal flow process in which a billet is pressed through a die consisting of two channels with equal cross-sections intersecting at an angle F. As the billet is pushed through the die, it deforms severely in simple shear mode.[4] ECAP presents the advantage of processing large samples while maintaining an
ALI AL-HADI KOBAISSY and MU’TASEM SHEHADEH are with the Mechanical Engineering Department, American University of Beirut, Beirut, 1107 2020, Lebanon. GEORGES AYOUB is with the Department of Industrial and Manufacturing Systems Engineering, University of Michigan-Dearborn, Dearborn, MI, 48128. Contact email: [email protected] WAHAZ NASIM, JAHANZAIB MALIK and IBRAHIM KARAMAN are with the Department of Materials Science and Engineering, Texas A&M University, College Station, TX 77843. Manuscript submitted March 24, 2020. Article published online August 25, 2020 METALLURGICAL AND MATERIALS TRANSACTIONS A
unchanged cross-sectional area. Numerous studies on ECAP were conducted to uncover the mechanisms of texture and microstructure alteration induced by grain refinement.[5–9] ECAP process parameters such as die angle F, number of passes, deformation routes, and the back-pressure considerably affect the grain refinement process and hence the texture and the microstructure.[5,10] The effect of the die angle was studied experimentally at room temperature (RT) on pure aluminum using four different die angles ranging from 90 to 157.5 deg.[11] For each die angle, the aluminum sample was processed by using several passes while maintaining the final imposed strain at ~ 4. Ultrafine equiaxed grains microstructure was achieved only with F = 90 deg. There are four basic types of routes in ECAP, namely, A, Ba, Bc, and C, as illustrated in Figure 1. Li and Mishin[12] reported that different deformation routes significantly affect the texture components intensity, which consecutively influence the anisotropic plastic response of aluminum billets. Ferrasse et al.[13] showed that the strength of ECAPed copper samples saturates with the grain refinement slowing down after four passes. In addition, for copper and aluminum billets ECAPed via routes A and B, ultrafine subgrain shear bands are observed within the parent grains. Another work by Shaeri et al.[14] reported that after 4 passes via routes A and Bc, the ECAPed aluminum presented a very fine microstructure with an average grain size of about 1 and 0.7 lm, respectively.
VOLUME 51A, OCTOBER 2020—5453
Fig. 1—(a) Simple schematic of the ECAP process, (b) re
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