Nanosecond Laser Modification of Nickel-Titanium Based Shape Memory Alloys

Abstract

Nickel-Titanium based Shape Memory Alloys (Ni-Ti SMAs), a group of special advanced engineering materials, are gaining popularity in industrial engineering and biomedical engineering for their superior properties. for example, amazing shape memory effects (SME), high strength, excellent corrosion and wear resistance, pseudoelasticity, outstanding biocompatibility and biodegradability. Industrial applications of Nickel-Titanium based SMAs include phone antennas, sensors and actuators in aerospace industry, automotive industries, and robotics. Biomedical engineering applications of this group of SMAs include cardiovascular field, neurosurgical field, orthodontic and orthopedic field. The fact that this group of SMAs are very sensitive to stress and mechanical tension makes it very difficult to be machined using conventional manufacturing processes. As a result, many research studies have focused on improving the machinability of this SMA using non-traditional manufacturing processes. In this study, the Continuum Surelite Class III nanosecond laser system with 1064 nm wavelength and 5 nanosecond pulse width is used to modify the surface of a Nickel-Titanium based SMA. The effects of laser pulse energy level and lens-to-samples distance on the crater and slot forming are evaluated. Single shot mode of the laser system is used to generate craters, and totally six laser pulse energy levels are used. In addition, three lens-to-sample distance values are selected. These six energy levels are 0.053 J, 0.122 J, 0.296 J, 0.415 J, 0.526 J, and 0.662 J, respectively. The three different lens-to-sample distance values are 150 mm, 170 mm, and 190 mm, respectively. The focal length of the lens is 150 mm. Continuous shot mode of the laser system is used to machine slots on the Ni-Ti based SMA. For slot forming, two energy levels (0.296 J and 0.662 J) and two lens-to-sample distance values (150 mm and 190 mm) along with two different overlapping ratios (0.75 and 0.95) are used. A 3D surface profilometer is used to study the variation of crater depth with laser parameters. The scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses are used to investigate surface topography, surface modification, and laser-induced elemental composition on the Ni-Ti based SMA surfaces. The crater diameter and depth were found to vary with the laser energy levels and lens-to-sample distances. The surface finish and topography were also found to be influenced by the laser parameters. Finally, a suitable range of parameters for improved surface finish and targeted surface modification have been identified for nanosecond laser processing of Nickel-Titanium based SMA.