Influence of Degree of Deformation on Static Recrystallization Texture and Compressive Strength of NiTiFe Shape Memory A
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TRODUCTION
BECAUSE of their perfect shape memory effect as well as excellent superelasticity, NiTi-based shape memory alloy (SMA) has been the most popular one of all the shape memory alloys (SMAs). Hot working[1,2] and thermomechanical processing[3–6] are two typical methods of manufacturing NiTi-based SMAs. The former focuses on the reduction of working loads and the improvement of ductility,[7,8] while the latter guarantees the accurate dimensional tolerance.[9,10] Both of the aforementioned methods have an important effect on the microstructures as well as the properties of NiTi-based SMAs. Over the past few years, more and more researchers have paid their attention to improving microstructures as well as properties of NiTi-based SMAs in a variety of ways, such as hot deformation, cold rolling,[11,12] high-pressure torsion (HPT),[13,14] cold drawing,[15,16] equal channel angular extrusion (ECAE),[17,18] canning compression,[19,20] and the YANQIU ZHANG and SHUYONG JIANG are with the College of Mechanical and Electrical Engineering, Harbin Engineering University, 145 Nantong Street, Harbin 150001, P.R. China. Contact e-mail: [email protected] BINGYAO YAN and MAN WANG are with the College of Materials Science and Chemical Engineering, Harbin Engineering University, 145 Nantong Street, Harbin 150001, P.R. China. Manuscript submitted April 8, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
combination of cold deformation and heat treatment.[21,22] Although these methods can significantly modify the microstructures or mechanical properties of NiTi-based SMAs, they are unable to obtain homogeneous microstructure in a material which possesses large size in all the three dimensions, and the obtained alloys often possess a poor combination of mechanical properties. In addition, most of the aforementioned investigations focused on microstructures and properties of NiTi-based SMAs based on hot deformation or cold deformation alone. Several studies have been concerned with the influence of cold deformation and subsequent heat treatment on the NiTi-based SMAs,[5,21,22] but all of them emphasized the heat treatment at lower temperatures. In fact, texture acts as a significant role in the mechanical properties of metals.[23–27] In addition, the texture of NiTi-based SMAs is still under the debate. In the case of rolling texture, Chang and Wu[28] studied the texture of cold-rolled Ni50Ti50 SMA at B2 state and found that the texture in this alloy consists of two components, i.e., ð331Þ½110 in rolling direction and ð111Þ½110 c-fiber in normal direction. Goryczka and Ochin[29] investigated the textures of two NiTibased (Ni50Ti50 and Ni47Ti50Co3 (at. pct)) SMA strips obtained by twin roll casting technique at B2 state, and they found that h100i fiber and {100}h001i sheet textures are dominant in both the alloys. Laplanche et al.[30] investigated the evolution of texture in a hot-rolled Ni51Ti49 SMA, and they found strong
{110}h110i a-fiber in rolling direction and {111}h110i c-fiber in normal direction. However, Suresh et al.[31] fo
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