ISSN 0031-918X, The Physics of Metals and Metallography, 2013, Vol. 114, No. 12, pp. 1069–1073. © Pleiades Publishing, Ltd., 2013. 1069 1 1. INTRODUCTION Hossein Nedjad et al. [1] reported preferred storage of screw dislocations in the equal-channel angular pressed 18Ni maraging steel recently. This report was in agreement with the storage of screw dislocations in hot- deformed germanium and silicon crystals reported by Siethoff and Schroeter [2] but in contrary to the pre- ferred storage of edge dislocations observed in severely- deformed commercially-pure copper and some alumi- num alloys [3–7]. The preferred storage of screw dislo- cations in the 18Ni maraging steel was interpreted in terms of the difficulties for cross slipping of screw dislo- cations augmented by reduced stacking faults energies and short range ordering due to the higher amounts of alloying additions such as cobalt. However, the possible role of the body-centered cubic (BCC) crystal symme- try remained controversial. It is noteworthy that those alloys that exhibit preferred edge dislocations invariably possess the face-centered cubic (FCC) crystal symme- try. Taking into account the effect of crystal symmetry on the preferred storage of dislocations, this paper was aimed at studying the relative fraction of stored edge and screw dislocations in the commercially pure copper and iron chips, which were severely-deformed by a high-energy planetary ball milling. Precision analysis of the integral breadths of X-ray diffraction peak profiles in accordance with the Will- iamson–Hall equations makes possible the determi- nation of the specific features of the dislocation struc- ture in severely-deformed metals. In the classical Wil- 1 The article is published in the original. liamson–Hall equation (Eq. 1), the integral breadths of the diffraction lines are plotted versus the diffrac- tion vector K. In the case of isotropic strain distribu- tion, those integral breadths fit well into a linear regression so that the intersection with vertical axis and the slope determine apparent size parameter and lattice distortions, respectively [8]. (1) where β is the integral breadth of an individual diffrac- tion line, d is the apparent size parameter, and ε is the lattice distortions. However, solids are often elastically anisotropic and, therefore, lattice distortions are usu- ally distributed anisotropically. Similarly, dislocations stored in the deformed metals cause anisotropic lattice distortions which, consequently, leads to non-mono- tonic increasing of the integral breadths of the diffrac- tion lines corresponding to the elastically soft direc- tions which, subsequently, makes the linear regression difficult and the classical equation inefficient. Alter- natively, the strain anisotropy is compensated in the modified Williamson–Hall equation by taking into account the average dislocation contrast factor ( ) as given in Eq. 2 [9]. (2) where ρ is the dislocation density, T is a constant depending on the density and effective outer cut-off radius of dislocations, b is the modulus of the Burgers vector of dislocations, and O is an unknown overall β 1 / d 2 ε K, + = c β 1 / d π T 2 b 2 ( ) 2 --------------- ρ 1 / 2 Kc 1 / 2 ( ) 2 O Kc 1 / 2 ( ) 4 , + + = A Comparison Between the Dislocation Structure of Ball-Milled Iron and Copper as Derived from the X-Ray Diffraction Peak Profile Analyses 1 F. Hosseini Nasab, S. Hossein Nedjad, and S. Karimi Faculty of Materials Engineering, Sahand University of Technology, P. O. Box 51335-1996, Tabriz, Iran e-mail: hossein@sut.ac.ir Received August 13, 2013 Abstract—X-ray diffraction line profile analyses were used for determination of the dislocation structure of ball-milled copper and iron samples. Plots of integral breadths of the diffraction line profiles in accordance with the classical Williamson–Hall equation clarified stronger strain anisotropy in iron than copper. By the analyses of the integral breadths in accordance with the modified Williamson–Hall equation, the relative fractions of edge and screw dislocations were determined. Prevailing dislocation structure of copper had edge character while those of iron showed mainly screw character. Keywords: X-ray diffraction, dislocation structure, ball-mill, Williamson–Hall, strain anisotropy DOI: 10.1134/S0031918X13220031 STRUCTURE, PHASE TRANSFORMATIONS, AND DIFFUSION