Investigation on the influence of underwater laser assisted micromachining process of NiTi (sheet) shape memory alloy

Abstract

This M.Tech thesis reports an investigation into underwater micromachining of NiTi shape memory alloy using Nd:YAG laser and associated physical phenomena. This study is motivated by a gap in the current knowledge in micromachining identified in an extensive literature review. NiTi has number of applications in the field of biomedical, aerospace, MEMS etc. because of its excellent shape memory, pseudoelasticity, biocompatibility and very high corrosion resistance. In case of micromaching the microdrilling, cutiing and microchanneling has been done of nitinol sheet. This study is primarily performed to investigate the microscopic behavior of NiTi sheet when microdrilled in open air and underwater environment using laser micromachining. The main aim is to develop a process, capable of achieving precise and high quality micro-drilling of the NiTi sheets. A nanosecond Pulsed-laser is focused on NiTi sheets (thickness 0.35 mm). Experiments were performed both in open air atmosphere and in running water. A Q-switched Nd:YAG laser at 532 nm with an output energy of 100 mJ was used with varying the number of pulses from 300 to 3000. The aim of these experiments of drilling nitinol sheet was to find the optimum laser processing parameters, such as the wavelength (λ), pulse energy (EP), fluence and number of laser pulses (N), for high quality drilling without material cracking and chipping. Secondly investigated the performance of cutting of nitinol sheet with long pulse at 1064 wavelength. Then investigated the microchanneling on nitinol with Qswitched pulsed laser. It was observed that the NiTi sheet can be ablatedefficiently with the running water when compared to open air environment. Surface morphology of the sample when performed in different environments investigated by Scanning electron microscopy (SEM). Thermo gravimetric analysis (TGA) is also carried out to determine thermal properties of NiTi. Heat affected zone were also investigated by Inverted Metallurgical Microscope and Micro-hardness tester. It was found that the ablation rate found in case of running water is 5 to 8 times more than that of open air environment. Finally, the results obtained by open air and underwater environment of the micromachining samples has been comparatively analyzed in this work study.