Laser shock wave assisted patterning on NiTi shape memory alloy surfaces

Abstract

An advanced direct imprinting method with low cost, quick, and less environmental impact to create thermally controllable surface pattern using the laser pulses is reported. Patterned micro indents were generated on Ni50Ti50 shape memory alloys (SMA) using an Nd:YAG laser operating at 1064 nm combined with suitable transparent overlay, a sacrificial layer of graphite, and copper grid. Laser pulses at different energy densities which generates pressure pulses up to 10 GPa on the surface was focused through the confinement medium, ablating the copper grid to create plasma and transferring the grid pattern onto the NiTi surface. Scanning electron microscope (SEM) and optical microscope images of square pattern with different sizes were studied. One dimensional profile analysis shows that the depth of the patterned sample initially increase linearly with the laser energy until 125 mJ/pulse where the plasma further absorbs and reflects the laser beam. In addition, light the microscope image show that the surface of NiTi alloy was damaged due to the high power laser energy which removes the graphite layer.

Periodic Heterogeneous Surface with Superhydrophilic/Superhydrophobic Stripes Processed by a Picosecond Laser

“…For surface shock wave, it is a type of discontinuous peak propagation in the medium, which will make the physical properties of the medium such as pressure, temperature, and density change by leaps. 23 Figure 4a shows the sand ripples that often appear in the desert. The physical mechanism for the formation of sand ripples can be attributed to the action of wind on loose sand.…”

“…Based on the mechanism of the formation of periodic structures by other scholars, ,− we believe that the formation of the periodic HS-s/sS is related to two main factors: one surface shock wave and one interference between SPP and the incident laser. For surface shock wave, it is a type of discontinuous peak propagation in the medium, which will make the physical properties of the medium such as pressure, temperature, and density change by leaps Figure a shows the sand ripples that often appear in the desert.…”