Recovery Behavior of Fe-Based Shape Memory Alloys under Different Restraints

Abstract

This paper presents the experimental results of an evaluation of the recovery behavior of Fe-based shape memory alloys (Fe-SMAs) under different restraints. For the study, three types of Fe-SMA (FSMA-A, FSMA-B, FSMA-C) were produced. As a result of the direct tensile test, the yield strength of the FSMA-A specimen was nearly 34% higher than the strength of FSMA-B and FSMA-C. Under free restraint, the recovery strains are 0.00956, 0.01445, and 0.01977 for FSMA-A, FSMA-B and FSMA-C specimens, respectively, after activation when the pre-strain is 0.04, and the heating temperature 200 °C. Under rigid restraint, the final recovery stresses are 518, 391 and 401 MPa for FSMA-A, FSMA-B, FSMA-C specimens after activation when a pre-strain of 0.04 and heating temperature 200 °C. Additionally, under the rigid restraint, the effect of pre-strain on the final recovery stress was insignificant, whereas the final recovery stress increased as the heating temperature increased. When Fe-SMA was constrained during cooling, the recovery stress is 50% lower than under rigid restraint. Hence, in order to develop a large recovery stress, Fe-SMA must be constrained during heating. In addition, a method for calculating the effective confining stress of the Fe-SMA coupler for pipe joining was proposed based on the experimental results.

Shape Memory and Mechanical Properties of Cold Rolled and Annealed Fe-17Mn-5Si-5Cr-4Ni-1Ti-0.3C Alloy

“…This means that the austenite starting temperature (As) is far lower than 150 °C. As demonstrated in a previous study [ 18 ], the onset of this alloy’s shape recovery took place immediately upon heating from RT, indicating that the As of the alloy is lower than RT. The recovery strain increased gradually by increasing the recovery heating temperature up to 400 °C in all the samples tested.…”

“…The present study is a continuation of the studies conducted by Hong et al [ 18 , 19 ]. As noted by Arabi-Hashemi et al [ 10 ], the yield strength is the main limiting factor to achieving significant recovery stress.…”

“…The sample annealed at 700 °C revealed the highest ε rec of 1.02%. The recovery strain of the 600-HT and 700-HT samples for T rec = 200 °C were comparable to the recovery strain of the hot-rolled sample [ 18 ]. However, a one-to-one comparison was not possible due to the different test configurations, i.e., the present study used bending tests with a pre-strain of 5.26% while the previous study used tensile tests with a pre-strain of 4%.…”

“…Post-aging heat-treatments have been carried out in these alloy systems to disperse the fine precipitates in the Fe-SMA microstructures. On the other hand, a new type of Fe-SMA containing TiC precipitate has recently been reported by Hong et al [ 18 ]. In this alloy, fine TiC precipitates were well dispersed in the microstructure after a hot-rolling process without any post-aging heat-treatment.…”

“…In this study, cold-rolling and annealing heat-treatment were additionally performed to further increase the Fe-SMA yield strength. The same hot-rolled Fe-SMA described previously [ 18 , 19 ] was used as the starting material. The microstructure, shape memory behavior, and mechanical properties of the cold-rolled and annealed Fe-SMA containing TiC were investigated.…”