Optimization of Fe-15Mn-5Si-9Cr-5Ni Shape Memory Alloy for Pipe and Shaft Couplings

We investigated whether Fe-Mn-Si shape memory alloys could be manufactured into machine parts and devices, in particular pipe and shaft couplings. Accounting for the optimal parameters affecting shape memory properties, i.e., the chemical composition, the amount of processing deformation, the annealing temperature, and the correlation between the reversibility of the martensitic transformation and the conditions of the microstructure (particularly the role of crystal defects), we found that maximum recovery in a Fe-15Mn-5Si-9Cr-5Ni alloy is achieved by rolling at 800 °C followed by annealing at 650 °C. Furthermore, we investigated certain properties that establish technological feasibility limits to industrial production, including alloy weldability and mechanical response. Bending and tensile specimen tests determinate the expected behavior of parts joined by welding. We also developed an original process to produce the couplings. The degree of shape recovery of the couplings manufactured by this method depends on the annealing temperature after welding. The couplings annealed at 800 °C recovered 83% of a 3.6% permanent diametrical expansion.