Tensile and bending deformation of Ni 3 Al heavily cold-rolled foil Satoru Kobayashi b, * , Masahiko Demura a , Kyosuke Kishida a , Toshiyuki Hirano a a National Institute for Materials Science, Tsukuba, Ibaraki, Japan b Department of Microstructure Physics and Metal Forming, Max Planck Institute for Iron Research, Max-Planck Str. 1, D-40237 Du ¨sseldorf, Germany Received 26 May 2004; received in revised form 25 August 2004; accepted 1 October 2004 Available online 26 November 2004 Abstract Local deformation characteristics of 95% cold-rolled Ni 3 Al foils were examined in tensile and bending tests along the rolling direction. The foils fracture without appreciable elongation in the tensile tests, while deform to 938 without cracking in the bending tests. However, the local deformation and fracture appear similarly in both of the tests: plastic deformation occurs in local regions by slip on the {111} planes where the slip deformation dominantly occurred during the prior cold rolling; cracks initiate along the shear bands which were formed during the cold rolling. The similarity of the local deformation was quantitatively confirmed by strain distribution measurements, i.e. the peak strain amounts to w10% just after crack initiation in both of the tests. These measurements verified that the extent of the local deformation is large enough to yield the good ductility in bending tests and not in tensile tests. q 2004 Elsevier Ltd. All rights reserved. Keywords: A. Nickel aluminides, based on Ni 3 Al; B. Plastic deformation mechanisms; C. Thin films; F. Mechanical testing 1. Introduction Ni 3 Al intermetallic compounds with ordered fcc (L1 2 type) structure have excellent high-temperature strength and oxidation/corrosion resistance [1–3]. A lack of ductility, which used to be the most serious problem, has been significantly overcome by micro alloying with boron [4,5], but heavy cold reduction is still difficult [6]. Recently we have succeeded in fabricating thin foils of binary Ni 3 Al by heavy cold rolling of the single crystals without intermedi- ate annealing [7–9]. The thinnest foils obtained so far are 20 mm in thickness with 99% reduction [9]. By using these foils, we have tried to fabricate the honeycomb structure [10], which is known as a lightweight structure with high strength and stiffness. The honeycomb structure made of Ni 3 Al foils is expected for use in high-temperature structural/functional applications. The cold-rolled foils possess relatively good bending ductility, which is large enough for making a corrugated form at room temperature [9,10]. The fracture elongation in bending amounts to the values from 4 to 7% on the tension- side surface in the case of the 95% cold-rolled foils [11]. In contrast, the foils fracture without showing macroscopic elongation in tensile tests [8,9], which is seemingly inconsistent with the good bending ductility. Since slip traces are observed near fracture region after tensile tests [9], it is obvious that the foils plastically deform in a limited region even under tensile stress condition. We consider that the role of the local deformation is the key to understanding the difference in macroscopic deformation between the tensile and bending tests. In this paper, local deformation characteristics were examined in both the tensile and bending tests, and the macroscopic deformation was discussed. 2. Experimental procedure A Ni 3 Al foil (87 mm in thickness) was fabricated by 95% cold rolling of a single-crystalline sheet with a nominal composition of binary Ni-24 at% Al in the same way as we previously reported [7–9]. The foil used in this study is the same as in the previous bending tests [11]. Tensile specimens with a gauge section of 10!5 mm were cut from the foil along the rolling direction (RD) by Intermetallics 13 (2005) 608–614 www.elsevier.com/locate/intermet 0966-9795/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.intermet.2004.10.002 * Corresponding author. Tel.: C49 211 6792 321; fax: C49 211 6792 333. E-mail address: kobayashi@mpie.de (S. Kobayashi).