Comparative Investigation on the Effects of Laser Annealing and Laser Shock Peening on the As-Manufactured Ni–Ti Shape Memory Alloy Structures Developed by Laser Additive Manufacturing

Abstract

An indigenously developed laser additive manufacturing (LAM) system was deployed to fabricate complex structures of Ni–Ti shape memory alloys. LAM is opted for samples development as it gives the advantage of fabricating complex structure precisely as per the requirement with good composition control. As-made samples were brought under two different surface processing techniques of laser annealing (LA) and laser shock peening (LSP). In general, LA is carried out to reduce the residual stress to improve the sample’s functional life, and LSP is done to induce compressive stress in the samples to improve the fatigue life and prevent the samples from fracture. Wide research has been done in the past to find the effects of LA and LSP on the samples to characterize the improvement of the samples in their respective accord. Both LA and LSP were carried out using pulsed green Nd:YAG laser. Since Ni–Ti is a shape memory alloy (SMA), there is no much exposure about the shape memory property of the sample before and after LA and LSP. In this chapter, an attempt has been made to investigate the surface morphology, crystallinity and shape memory effect of Ni–Ti fabricated by LAM. Obtained results are homogenous microstructure, good crystalline nature and better shape memory effects through LA or LSP. The surface morphology, phase transformation temperature and microstructure of laser annealed Ni–Ti structures were studied with scanning electron microscopy (SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). Laser energy density of 1100 mJ/cm2 at 532 nm wavelength was used for LA. Same laser energy density at 1064 nm wavelength was used for LSP. Novel output regarding the shape memory nature of the materials was obtained.