Design of devices and manufacturing of Fe-Mn-Si shape memory alloy couplings

Abstract

We have studied an Fe-15Mn-5Si-9Cr-5Ni (wt.%) shape memory alloy produced by casting in sand moulds. After processing by rolling at 800° C followed by annealing at 650° C, the structure contains a high density of stacking faults and high strength austenite. When a stress is applied to the material, a reversible martensitic transformation activates before the austenite deforms plastically. Under these conditions, the material recovers about 95% of a 3% permanent deformation. The mechanical properties were measured by tensile tests, giving a yield strength of 350 MPa, an ultimate strength of 880 MPa and 16% total elongation to fracture. Furthermore, the alloy has good weldability using the GTAW method. No macro or micro defects were observed, but there is a 15% deterioration of the shape memory properties due to a heat affected (HAZ) and welded zone (WZ), as measured with bend specimens. In this work, we studied the formability of the material, finding very good performance in simple bending tests. We also present a method for manufacturing couplings by forming and welding, designing forming devices and obtaining the first prototypes. Finally, we evaluated the shape memory properties of the manufactured couplings, finding 83% recovery of a 3.6% diameter expansion. This amount of recovery is suitable for various industrial applications.