Laser-Induced Forward Transfer of Ni-rich NiTi Alloys for Shape Memory Applications

Laser-induced forward transfer (LIFT) is a direct-write technique that uses laser pulses to sequen-tially deposit small volumes of a material from one substrate to another. It is a proven deposition process to fabricate complex functional micro-structures. Shape memory alloys (SMAs) are active materials that can be deformed at low temperatures and return to their original parent shape under the influence of appropriate thermomechanical conditions (i.e. by changing the temperature and/or the stress). Functional grading of SMA characteristics by precisely controlling the composition locally can provide a complex actuation response of the overall structure to external stimuli (stress, temper-ature) thereby significantly widening applications. Conventionally, SMAs are bulk heat-treated dur-ing the manufacturing process to ensure homogenization, eliminate internal defects, and, by implica-tion, alter transformation temperatures. High power lasers can provide localized heating coupled with high heating and cooling rates, and hence provide the opportunity to control the formation of micro-structures and the resulting phase, but this technique has not yet been fully explored with SMAs. In this paper, we explored this potential by fabricating NiTi based alloys using LIFT and then subjecting them to heat treatment using a nanosecond laser.