Superficial changes on the Inconel 600 superalloy by picosecond Nd:YAG laser operating at 1064, 532, and 266 nm: Comparative study J. STAŠIC ´ , 1 B. GAKOVIC ´ , 1 M. TRTICA, 1 T. DESAI, 2 AND L. VOLPE 3 1 VINC ˇ A Institute of Nuclear Sciences, University of Belgrade, Belgrade, Serbia 2 National Research Institute for Applied Mathematics, Jaynagar, Bangalore, India 3 Universita degli Studi Milano Bicocca, Dipartimento di Fisica “G. Occhialini,” Milano, Italy (RECEIVED 14 October 2011; ACCEPTED 22 December 2011) Abstract A comparative study of superficial changes on the superalloy Inconel 600, induced by a picosecond Nd:YAG laser operating at 1064, 532, and 266 nm, is presented. All of the laser wavelengths, as well as the used fluences of 2.5 (1064 nm), 4.3 (532 nm), and 0.6 J/cm 2 (266 nm) were found to be adequate for inducing surface variations. Quite different surface features were produced depending on the laser wavelength used. The measured surface damage thresholds were 0.25, 0.13 and 0.10 J/cm 2 for 1064, 532, and 266 nm, respectively. Drastic differences, in function of the wavelength used, were recorded for the crater depths, as well the appearance of hydrodynamic effects and periodic surface structures. Differences in crater depths were explained via an easier propagation of the first harmonic laser radiation (1064 nm) through the ejected material and plasma compared to a radiation at 532 and 266 nm. Finally, changes in the surface oxygen content caused by ultrashort laser pulses were considered. Keywords: Laser ablation; Periodic surface structures; superalloy Inconel; Surface morphology 1. INTRODUCTION Nickel-based superalloy are in a class of special alloys charac- terized by extraordinary properties. These alloys possess high temperature and mechanical strength, great corrosion resist- ance, especially at elevated temperatures, outstanding resist- ance to pitting, good heat conductivity, resistance to aggressive atmosphere (e.g., acids). Due to these excellent fea- tures, the alloys are attractive for numerous applications in electrical, chemical and food industry, aero and space engin- eering, etc. Moreover, superalloy can be used in the nuclear complex, in the technology of fission as well as fusion reactors (In et al., 1995; Busharov et al., 1977). Thus, the quality of fusion plasma in a thermonuclear device depends not only on the reactor design, but also on the proper selection of reac- tor vessel wall material, especially plasma facing materials (Sannazzaro et al., 1991). Nickel-based superalloy Inconel 600, high quality steels, etc., can be used as plasma facing materials. These materials are, among other, exposed to fluxes of electromagnetic radiation in the reactor so their behavior can be simulated in the laboratory using high inten- sity laser radiation. Inconel superalloy was recently success- fully applied in medicine as an implant for cardiovascular usage (Grifka et al., 2008). It is well known that the implant surface, as well as its state, influences the level of biocompat- ibility with human body. One of the promising treatments of implants, including Inconel 600, is laser treatment. Finally, specific applications, e.g., aerospace engineering, require per- foration of small apertures which, apart from conventional techniques, can be achieved by lasers (Chen & Liu, 1999). Generally, surface modifications of different nickel-based superalloys using laser systems are of great fundamental and practical interest. Studies on the interaction of laser beam with these alloys were intensified in the last decade. Various laser systems, such as pulsed Nd:YAG (Chen et al., 1996; Bugayev et al., 2006), excimer (Pantelis & Psyllaki, 1996), pulsed and continues wave CO 2 (Zysk, 1990; Hong et al., 2008) and Ti:sapphire lasers have been used for these pur- poses (Feng et al., 2005; Semaltianos et al., 2009). Investigations of the interaction of pulsed picosecond laser beam with nickel-based superalloys particularly Inconel 600, which is just the focus of this research, are scarce in literature. 249 Address correspondence and reprint requests to: Jelena Stašic ´, VINC ˇ A In- stitute of Nuclear Sciences, P.O. BOX 522, 11001 Belgrade, Serbia. E-mail: jelsta@vinca.rs Laser and Particle Beams (2012), 30, 249–257. © Cambridge University Press, 2012 0263-0346/12 $20.00 doi:10.1017/S0263034611000899