Laser microwelding as a novel alloying process to fabricate NiTiPtIr high temperature shape memory alloys

High temperature shape memory alloys (HTSMAs) manufacturing requires a complex processing procedure. This work presents the application of microwelding as a simple, but a novel method to process NiTiPtIr HTSMAs. Laser microwelding was applied to fuse a NiTi tube cored with a PtIr wire to fabricate a NiTiPtIr alloy wire. X-ray microtomography was used to develop the process and confirm the formation of a uniform NiTiPt phase in the wire volume. After heat treatment, the processed NiTiPt material showed considerable superelasticity at 250 °C with just 0.7% residual strain for a maximum imposed strain of 4%. TEM observations revealed the presence of B19 and a smaller fraction of B19' martensitic structures in the matrix due to minor changes in the Pt concentration. This laser microwelding enabled selective alloying for the fabrication of NiTiPtIr which opens the door toward a more straightforward production method for ternary NiTi-based HTSMAs.