Nanostructured NiTi Shape Memory Alloy Via Ni/Ti Nanolamination
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ic NiTi is the most commonly used shape memory material due to its unique features,[1] such as high strength, superelasticity, and excellent shape memory effect. Usually, NiTi shape memory alloys (SMAs) are mainly produced by ingot wrought processes. However, the production of NiTi thin sheets or wires requires multiple complex annealing between the wrought passes. The necessity of annealing is a result of its inferior workability of NiTi. Powder metallurgy is an alternative processing technique; however, the interstitial contamination during powder consolidation processing is difficult to avoid. If elemental powders are used in powder sintering, many other intermetallic compounds may be formed; these intermetallics are not desired for the achievement of shape memory and superelasticity effect.
JINTAO ZHANG, HUA DING, and MINGHUI CAI are with the School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China. Contact e-mail: [email protected] NING ZHANG, HAITAO QU, SHUXIA LI, and HONGLIANG HOU are with the Beijing Aeronautical Manufacturing Technology Research Institute, Beijing 10024, China. PENG CAO is with the Department of Chemical and Materials Engineering, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand. Contact e-mail: [email protected] Manuscript submitted July 24, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
One alternative manufacturing method for NiTi sheets is via multilayered thin Ni/Ti laminates.[2] In this method, a stack of multiple layers of alternating Ti and Ni are subjected to cold or warm rolling. The as-rolled multilayered laminates are then annealed to achieve alloying and/or further consolidation. Other similar techniques include explosive welding,[3] accumulative roll bonding (ARB),[4,5] extrusion,[6] and physical vapor deposition (PVD).[7] Among them, ARB is a promising route since it is a severe plastic deformation (SPD) process, which leads to ultrafine microstructure. In addition, it is a cost-effective and continuous production process for producing large bulk materials.[8] Tomus et al.[9] reported that the NiTi SMA was obtained after the stacked Ni/Ti laminates were rolled down to 50 lm from ~ 28 mm (i.e., with a thickness reduction of ~ 99.8 pct), followed by a diffusion heat treatment at 800 C (1073 K) for 10 hours. Ding et al.[10] reported similar results in a Ni/Ti stack, which was subjected to a stepwise cold rolling with an overall thickness reduction of 97 pct and followed by a similar annealing process. Both Ding et al. and Tomus et al. attributed the low annealing temperature to the ultra-thin Ti and Ni foils after rolling. It is expected that, if the Ni/Ti laminates were refined to a nanometer scale, the subsequent diffusion treatment (annealing) temperature and time could be further reduced, and the nanostructured NiTi SMA could be retained. The objective of the present research is, therefore, to develop an accumulative roll bonding process to produce nanostructured NiTi SMA. It is noted that in the works of Ding et
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