Superelastic Fe-based Shape Memory Alloy Cables

A new class of Fe-based SMA cables is examined as a candidate to provide high performance per cost unit, design flexibility, and damage resistance into industrial applications and to show that favorable wire properties can be scaled into larger assemblies. So far, NiTi SMA cables have been studied in detail and have shown better flexibility and strain-recovery properties than similar diameter monolithic SMA bars. However, the inherent material cost and difficulties in welding and joining of NiTi SMA cables may limit their use at scale in some applications. In this work, we have developed an inexpensive Fe-Mn-Al-Ni SMA cable. Cables are fabricated into a simple 1x7 construction with an individual wire diameter of 0.5 mm. Abnormal grain growth heat treatments were performed to generate large grains and nano-sized precipitates are formed in the matrix after precipitation heat treatments at 200C for 3h. Microstructural features of the wires were investigated using electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM). Grain growth methods and crystallographic texture in these Fe-based SMA cables are discussed. Tensile cyclic tests were performed at room temperature until failure to determine critical stress for stress induced martensitic transformation (CSSIM), stress hysteresis, superelastic strain and irrecoverable strain. Results are compared against similarly constructed NiTi and stainless-steel cables.