Texture Evolution as Determined by In situ Neutron Diffraction During Annealing of Iron Deformed by Equal Channel Angula
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EQUAL-CHANNEL angular pressing (ECAP) is a versatile severe plastic deformation (SPD) technique used to produce bulk metals and alloys with ultrafine grain structure (UFG), i.e., grain sizes below 1 lm.[1] ECAP allows processing of round, rectangular-, and square-shaped billets without changing their initial cross section, allowing repeated application of the process to accumulate large strains. Deformation at the intersection of the channels is assumed to occur by simple shear[2,3] and the final microstructure and texture is dependent on the chosen processing route, the angle between the two channels, the die geometry, and the number of passes (accumulated strain).[1,4] Commonly ECAP-processed materials show weak-to-moderate texture intensities, in particular for route Bc, where the billet is turned 90 deg clockwise around the extrusion axis between ECAP passes.[5–7] The route Bc is known to produce microstructures with a predominance of fineequiaxed grains compared to predominantly elongated grains resulting from other ECAP routes.[8] H.R.Z. SANDIM, Associate Professor, and M.J.R. SANDIM, Assistant Professor, Faculty, are with the Escola de Engenharia de Lorena, Universidade de Sa˜o Paulo, Lorena 12600-970, Brazil. Contact e-mail: [email protected] R.E. BOLMARO, Professor, is with the Instituto de Fı´ sica Rosario, CONICET - UNR, Rosario, 2000, Argentina. R.A. RENZETTI, Faculty, formerly with the Escola de Engenharia de Lorena, Universidade de Sa˜o Paulo, is now with the Universidade Federal de Itajuba´, Itajuba´, Brazil. K.T. HARTWIG, Professor, is with the Department of Mechanical Engineering, Texas A&M University, College Station, TX, 778433123. S.C. VOGEL, Researcher, is with the Los Alamos Neutron Science Center, LANSCE-LANL, Los Alamos, NM 87545. D. RAABE, Professor, is with the Max-Planck-Institut fu¨r Eisenforschung (MPIE), Du¨sseldorf 40237, Germany. Manuscript submitted September 17, 2013. Article published online July 4, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
The literature provides a few studies on the texture evolution of ECAP-deformed materials using neutron diffraction,[9–11] as well as on their thermal stability, with a clear predominance of fcc (face-centered cubic) metals and alloys.[12–16] Only a few papers report on the microstructural characterization and thermal stability of bcc (body-centered cubic) metals deformed by ECAP including niobium,[17,18] tantalum,[19] and tungsten,[20] as examples of ECAP processing in refractory metals, and also in low carbon (LC), ultra-low carbon (ULC), and interstitial-free (IF) steels.[21–26] Similar types of ultrafine microstructures processed via SPD in bcc materials can also be obtained by high pressure torsion[27–30] or accumulative roll bonding.[31–33] The deformation structure of ECAP-processed materials is far from equilibrium and contains a high area fraction of interfaces (low and high angle boundaries), as well as free dislocations.[1] The higher the number of ECAP passes in metals, the higher is the fraction of boundaries with mi
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