Dislocation study of ARMCO iron processed by ECAP
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Dislocation study of ARMCO iron processed by ECAP Jairo Alberto Muñoz1,a, Oscar Fabián Higuera1, 2, b , José María Cabrera1, 3, c 1
Department of Materials Science and Metallurgical Engineering ETSEIB, Universidad Politécnica de Catalunya, Av Diagonal 647, 08028 Barcelona, Spain. 2 3
a
Faculty of Mechanical Engineering, Universidad del Atlántico, Colombia
Fundació CTM Centre Tecnológic, Pl. de la Ciencia 2, 08243, Manresa, Spain.
[email protected], [email protected], [email protected]
ABSTRACT The aim of this work was to study the deformation behavior of an Armco iron after severe plastic deformation by equal channel angular pressing (ECAP). Particular attention was paid to predict the dislocation density by different approaches like the model proposed by Bergström. Experimental measures of dislocation density by different techniques are used in the discussion. Cylindrical samples of ARMCO iron (8mm of diameter, 60mm of length) were subjected to ECAP deformation using a die with an intersecting channel of Φ=90º and outer arc of curvature of ψ= 37° die. Samples were deformed for up to 16 ECAP passes following route Bc. The mechanical properties of the material were measured after each pass by tensile tests. The original grain size of the annealed iron (70 μm) was drastically reduced after ECAP reaching grain sizes close to 300nm after 16 passes. INTRODUCTION During large plastic deformation of metals and alloys, the original grain structure develops a microstructure on a much smaller scale. Ultra fine grain (UFG) materials are quite attractive due to the ultrahigh strength they can attain, which is more than twice that of their coarse grained counterparts. The movement of dislocations constitutes the fundamental basis for understanding the plastic behavior of crystalline materials [1], and this fact becomes specially important in analyzing the plastic behavior of UFG materials, where controversial results can be found in the literature concerning the role played by dislocations and their limited motion capability. Under this point of view scarce studies can be found in the literature concerning the dislocation density evolution during a severe plastic deformation process. Length scales associated with dislocation structures range from grain-size features (typically 0.1–10 mm) down to perhaps tens of atoms (1–10 nm). Because of this large range, a good characterization normally requires a combination of techniques [2]. Dislocation density (measured as number of lines per unit area, or length per unit volume) in thin foils can be
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measured directly using TEM. TEM measurements are experimentally challenging (problems include sample preparation, and finding imaging conditions for all dislocations), and thin films may not be representative of bulk material . X-ray line
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