Non-basal slip in Ni 3 (Ti, Nb) and Ni 3 (Ti, Al) single crystals with various long-period stacking ordered structures Koji Hagihara a,⇑ , Tetsunori Tanaka b , Hitoshi Izuno a , Yukichi Umakoshi b , Takayoshi Nakano b a Department of Adaptive Machine Systems, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan b Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan Received 7 March 2013; received in revised form 4 April 2013; accepted 4 April 2013 Available online 1 May 2013 Abstract Variations in operative non-basal slip systems in Ni 3 Ti-based long-period stacking ordered (LPSO) phases with the stacking sequence of the closely packed planes and the temperature dependence of the critical resolved shear stress (CRSS) were investigated. It was con- firmed that the f  1100g prism slip is operative in most of the LPSO phases with hexagonal unit cells, while the f  1011g pyramidal slip is operative in 9R LPSO phase with rhombohedral unit cell. The mechanism controlling the deformation by non-basal slip at low temper- atures is considered to be governed by the energy of the antiphase boundary (APB) formed between the a=6h11  20i superpartial dislo- cations in accordance with the kink pair nucleation mechanism proposed by Mitchell et al. The dependence of variations in CRSS for non-basal slip on the Nb content was found to be much smaller than that for basal slip. The present results suggest that the mobility of dislocations on the non-basal plane hardly affected the behavior of yield stress anomalies (YSAs) caused by basal slip in Ni-based LPSO phases, although the Kear–Wilsdorf locking process, which is responsible for the YSA by basal slip, accompanies microscopic cross-slip from the basal slip plane onto the non-basal planes. Ó 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Plastic deformation; Dislocation; Intermetallic compound; Mechanical properties; Long-period stacking ordered structure 1. Introduction Ni 3 X type intermetallic compounds are known to crys- tallize in various geometrically close packed (GCP) crystal structures depending on the type of the X atom. We found that the positive temperature dependence of the yield stress termed the yield stress anomaly (YSA) appears not only in L1 2 -Ni 3 Al [1,2] but also in other GCP phases, such as D0 a - Ni 3 Nb [3], D0 24 -Ni 3 Ti [4], and D0 19 -Ni 3 Sn [5]. This is because all these systems have a common closely packed (CP) plane which corresponds to the {1 1 1} plane in face- centered cubic (fcc) and (0 0 0 1) in hexagonal close-packed (hcp) structures, and the motion of dislocation on the CP plane causes the YSA. Most of the models proposed to explain the YSA in L1 2 compounds rely on exhausting the mobile dislocations by the Kear–Wilsdorf (K–W) lock- ing mechanism [1,2,6–9]. K–W locking in L1 2 materials occurs by thermally activated cross-slip of the leading 1=2h1  10i screw partial from the {1 1 1} primary slip plane (CP plane) onto the {0 0 1} plane (non-CP plane). The driv- ing force for cross-slip is considered to be contributed in part by the difference in energy of the antiphase boundary (APB) formed between superpartial dislocations between the CP and non-CP planes [7,8]. To confirm this experi- mentally in our previous studies we identified plastic defor- mation behavior accompanied by basal slip in various long-period stacking ordered (LPSO) compounds in the Ni–Ti–Nb ternary system [10,11]. The LPSO phase has the same common CP plane as the above-mentioned GCP compounds, but its stacking sequence is lengthened along the c-axis. In the Ni 3 Ti solid solution region several 1359-6454/$36.00 Ó 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.actamat.2013.04.008 ⇑ Corresponding author. Tel.: +81 6 6879 7434; fax: +81 6 6879 4174. E-mail address: hagihara@ams.eng.osaka-u.ac.jp (K. Hagihara). www.elsevier.com/locate/actamat Available online at www.sciencedirect.com Acta Materialia 61 (2013) 4365–4373