Formation of two-way shape memory effect in NiTi alloy using pulsed laser irradiation

We report an advanced laser imprinting technique with low cost, quick and minimal environmental impact. Microindents were obtained on Ni₅₀Ti₅₀ (at. %) SMAs using an Nd:YAG laser with 1064 nm wavelength at 10 Hz. Laser pulses at selected fluences were focused on the NiTi surface and generated pressure pulses of up to a few GPa. Scanning electron microscope (SEM) and optical microscope images showed that surface patterns with tailorable sizes can be obtained, where the depth of the patterns increased with laser power and irradiation time. Upon heating, the maximum depth recovery ratio of 30 % was observed. Recovery ratio decreased and stayed around 15 % when the amount of time and thus the indent depth was increased. Laser-induced shock wave propagation inside the material was simulated and the stress wave was shown to closely follow the rise time of the laser pulse to its peak value and initial decay. Rapid attenuation and dispersion of the stress wave were observed.