Experimental Investigation of Nanosecond Laser Modification of Bulk Metallic Glass

Abstract

Bulk metallic glass (BMG), a comparatively new engineering material, is gaining popularity for its amorphous structure, improved mechanical properties, (i.e., high elasticity, hardness, and fracture toughness), and corrosion resistance. Some of the recent and prospective areas of applications of BMGs include biomedical implants, nuclear reactor, and space and electronic applications. As a result, machinability and surface treatment of BMGs have become an important area of research. In this study, a nanosecond laser with 1064 nm wavelength is used to modify the surface of a Zr-based bulk metallic glass Vitreloy 1b. (Zr67Cul0.6Ni9.8Ti8.8Be3.8). The effects of laser pulse energy level and the lens-to-sample distance on the crater and slot forming are assessed. 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. The three different lens-to-sample distance values are 150 mm, 170 mm, and 190 mm. The focal length of the lens is 150 mm. Continuous shot mode of the laser system is used to machine slots on the BMG. For slot forming, two energy levels (0.296 J and 0.662 J) and two distance values between the lens and the workpiece (150 mm and 190 mm) along with two different overlapping ratios (0.75 and 0.95) are used. An interesting observation on the modified surface of BMG is the ripple formation at the edge of the craters, while the center of the crater has comparatively a smoother surface. The modified surface using focal length (150 mm) generated craters with higher number of wrinkles or ripples at the edge compared to the other distances between the lens and the workpiece. The characteristic of formation of ripples remains the same for slot forming also, although the intensity of ripple formation or number of ripples is decreased. Finally, 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, ripple formation, surface modification, and laser-induced elemental composition on the BMG surfaces.