Abstract
The effect of interaction of lasers having different spectral and temporal profiles with titanium on the weld surface quality is investigated by high-speed imaging and optical emission spectroscopy at atmospheric pressure in argon environment. High-speed imaging of the plume reveals that plume is produced during the laser pulse. Decrease in plume size and expansion rate is observed for those lasers whose spectral profiles overlap with more number of neutral atomic titanium transitions (Ti I) owing to increasing rate of reabsorption of the laser pulse primarily by the neutral titanium atoms present in the plume. Darkness around the laser spot on the titanium surface observed due to deposition of the nanoparticles increases with decrease in size and expansion rate of the plume which indicates that reabsorption of the laser pulse is the main cause of dark colouration of the surface. The bright appearance of a part of the plume produced by one laser at which another laser whose spectral profile cover many Ti I transitions is passed confirms the reabsorption process. Clean appearance of the surface around the laser spot along with enhancement of the plume size and expansion rate is observed for lasers with customized spectral profiles which do not overlap with any Ti I transitions. Modulation of the temporal profile can moderately improve the plume expansion rate and reduce the darkness around the laser spot provided that the laser spectral profile does not overlap with many Ti I transitions, particularly, with those whose energy of lower levels is less than 3 eV.
Highlights
Titanium and its alloys have widely been used in aviation, automotive, aerospace, biomedical, shipbuilding, petrochemical, nuclear and power generation industries due to their high strength, low density, high fracture toughness, fatigue strength and resistance to crack propagation, superior biocompatibility, high temperature mechanical properties, and excellent corrosion resistance [1,2,3]
We have comparatively investigated the effect of interaction of four different lasers having different spectral and temporal profiles on the surface quality of titanium with in-situ characterization of ejected plume by high-speed imaging (HSI) and optical emission spectroscopy (OES)
Energy Dispersive X-ray Spectroscopy (EDS) analysis and SEM images shown in Fig. 3 reveal that dark colour around the laser spot is caused by the deposition of titanium nanoparticles whose size ranges from 5 to 260 nm with an average size of about 70 nm
Summary
Titanium and its alloys have widely been used in aviation, automotive, aerospace, biomedical, shipbuilding, petrochemical, nuclear and power generation industries due to their high strength, low density, high fracture toughness, fatigue strength and resistance to crack propagation, superior biocompatibility, high temperature mechanical properties, and excellent corrosion resistance [1,2,3]. With the advancement of different applications of titanium and its alloys in various industries, several welding techniques such as tungsten inert gas (TIG) welding, laser welding, laser-hybrid welding, electron beam welding and friction welding have been developed [2]. Laser welding has been paid significant attention due to its high energy concentration, ease of realizing automation and rapid processing, high precision, high weld quality with narrowest fusion and heat affected zones, high efficiency and excellent flexibility [1,4]. In laser welding process of metals, a high power laser beam is focused onto the metal pieces for joining which results in melting, evaporation and resolidification. Many different kinds of lasers such as CO2, Nd:YAG, diode, disk, and fiber lasers have been employed as heat source to realize the high quality weld.
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