Characterizing the nano-structure and defect structure of nano-scaled non-ferrous structural alloys Iman Ghamarian a,b, ⁎, Peyman Samimi a,b,c , Yue Liu a,b,c , Behrang Poorganji d , Vijay K. Vasudevan d , Peter C. Collins a,b,c a Department of Materials Science and Engineering, Iowa State University, Ames, IA 50011, USA b Department of Materials Science and Engineering, University of North Texas, Denton, TX 76203, USA c Center for Advanced Non-Ferrous Structural Alloys, an NSF-I/UCRC between the University of North Texas (Denton, TX, 76203) and the Colorado School of Mines (Golden, CO, 80401), United States d Department of Mechanical and Materials Engineering, University of Cincinnati, Cincinnati, OH 45221, USA abstract article info Article history: Received 12 May 2015 Received in revised form 1 October 2015 Accepted 4 October 2015 Available online 9 October 2015 Keywords: Nanoscale orientation microscopy Nanotwin characterization ASTAR™ Precession electron diffraction Spatial distribution of geometrically necessary dislocations Severely deformed metallic materials The presence and interaction of nanotwins, geometrically necessary dislocations, and grain boundaries play a key role in the mechanical properties of nanostructured crystalline materials. Therefore, it is vital to determine the orientation, width and distance of nanotwins, the angle and axis of grain boundary misorientations as well as the type and the distributions of dislocations in an automatic and statistically meaningful fashion in a relatively large area. In this paper, such details are provided using a transmission electron microscope-based orientation microscopy technique called ASTAR™/precession electron diffraction. The remarkable spatial resolution of this technique (~2 nm) enables highly detailed characterization of nanotwins, grain boundaries and the configuration of dislocations. This orientation microscopy technique provides the raw data required for the determination of these parameters. The procedures to post-process the ASTAR™/PED datasets in order to obtain the important (and currently largely hidden) details of nanotwins as well as quantifications of dislocation density distributions are described in this study. © 2015 Elsevier Inc. All rights reserved. 1. Introduction It is widely accepted that during the interaction of microstructure and defects, size effects begin to dominate when the scale of the micro- structural features are small or when the number of defects is large. Thus, for nanostructured crystalline materials the presence and interac- tion of nanotwins, geometrically necessary dislocations, and grain boundaries play a key role in the overall balance of mechanical proper- ties. Nanostructured metallic materials often exhibit superior properties such as high yield strength and fatigue resistivity with an attending debit in tensile ductility [1]. It may be possible to improve the overall balance of properties by tailoring the microstructural features, along with composition. For example, the introduction of a large volume of nanotwins (which form in metals with low or intermediate stacking fault energy such as Ni and Cu [2]) simultaneously improves often competing mechanical properties (e.g. yield strength and ductility) without negatively or considerably affecting other physical properties, e.g., electrical conductivity [3]. This is achieved by promoting a ductile failure mode via the reduction of the spacing between multiple twins to an average inter-twin distance of b 15 nm [4]. In reality, there is a significant lack of understanding of the phenom- enon that occurs when the size-scale of the microstructure is quite small relative to the defect size. Indeed, with respect to plasticity there can be seemingly confusing and contradictory trends. For example, it is shown that for a case where the distance (d) between nanotwins is larger than 150 nm, the Hall–Petch equation is valid and the hardness follows d -1/2 dependence. However, for smaller distance values (e.g. d b 100 nm), a d -1 dependence was observed. This deviation has been rationalized based on the nanotwin–dislocation interactions [5]. Another study by Zhao and LeSar showed that for thin grains that comprise a thin film, the exponent of the Hall–Petch relationship (a) for yield strength was highly dependent upon both the diameter as well as thickness. For thin grains (i.e., t b 250 nm), the exponent a is ~0.27, whereas for thick grains (i.e., t N 1500 nm), a is ~0.51 [6]. Generally, the exponent term of the Hall–Petch equation associated with metallic materials may vary from 0.2 to 1 [7]. The breakaway from an ‘idealized’ Hall– Petch relationship can be assigned to various scenarios (e.g., rapid diffusional creep [8], presence of flaws [9]) which govern the Materials Characterization xxx (2015) xxx–xxx ⁎ Corresponding author at: Department of Materials Science and Engineering, Iowa State University, Ames, IA 50011, USA. E-mail address: imanghamarian@yahoo.com (I. Ghamarian). MTL-08047; No of Pages 10 http://dx.doi.org/10.1016/j.matchar.2015.10.002 1044-5803/© 2015 Elsevier Inc. All rights reserved. Contents lists available at ScienceDirect Materials Characterization journal homepage: www.elsevier.com/locate/matchar Please cite this article as: I. Ghamarian, et al., Characterizing the nano-structure and defect structure of nano-scaled non-ferrous structural alloys, Mater Charact (2015), http://dx.doi.org/10.1016/j.matchar.2015.10.002 Materials Characterization