J. Stasic

Superficial changes on the Inconel 600 superalloy by picosecond Nd:YAG laser operating at 1064, 532, and 266 nm: Comparative study

AbstractA comparative study of superficial changes on the superalloy Inconel 600, induced by a picosecond Nd:YAG laseroperating 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. Quitedifferent surface features were produced depending on the laser wavelength used. The measured surface damagethresholds were 0.25, 0.13 and 0.10 J/cm 2 for 1064, 532, and 266 nm, respectively. Drastic differences, in function ofthe wavelength used, were recorded for the crater depths, as well the appearance of hydrodynamic effects and periodicsurface structures. Differences in crater depths were explained via an easier propagation of the first harmonic laserradiation (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

Pulsed TEA CO2 Laser Irradiation of Titanium in Nitrogen and Carbon Dioxide Gases

Surface changes created by interaction of transversely excited atmospheric carbon dioxide (TEA CO2) laser with titanium target/implant in nitrogen and carbon dioxide gas were studied. TEA CO2 laser operated at 10.6 μm, pulse length of 100 ns and fluence of ∼17 J/cm2 which was sufficient for inducing surface modifications. Induced changes depend on the gas used. In both gases the grain structure was produced (central irradiated zone) but its forms were diverse, (N2: irregular shape; CO2: hill-like forms). Hydrodynamic features at peripheral zone, like resolidified droplets, were recorded only in CO2 gas. Elemental analysis of the titanium target surface indicated that under a nitrogen atmosphere surface nitridation occurred. In addition, irradiation in both gases was followed by appearance of plasma in front of the target. The existence of plasma indicates relatively high temperatures created above the target surface offering a sterilizing effect.

Surface modification of a-CN/TiAlN double layer coating on ASP 30 steel induced by femtosecond laser with 10 13 –10 14 W/cm 2 intensity in vacuum

A double layer a-CN/TiAlN coating deposited on ASP30 steel substrate was irradiated by femtosecond laser and surface modification effects were observed. Moderate laser intensities used were in the range of 10 14 –10 13 W/cm 2 , while the total thickness of double layer coating was 4.8 µm (a-CN = 0.6 and TiAlN = 4.2 µm). Laser-induced changes of the surface showed dependence on laser intensity and number of accumulated pulses. Irradiations at the highest intensity resulted in preservation of one or both layers up to 10 pulses, while at lower intensity (10 13 W/cm 2 ) a-CN layer is removed after several pulses and TiAlN is preserved up to 50 pulses. Evaluated damage threshold of the target was 0.49 J/cm 2 . Lower laser intensity irradiation produced periodic surface structures (LIPSS) over the entire irradiated spot with periodicity of ~700 nm, almost in agreement with the laser wavelength used. Irradiations carried out at the highest laser intensity (10 14 W/cm 2 ) and laser pulse count of ≥50 resulted in the creation of crater like damages with depth up to 20 µm. Craters were conically shaped, implying intensive processes which took place at the surface. Generation of LIPSS as well as craters can be of great interest for contemporary technologies.