Modifications of AISI 1045 steel by picosecond Nd:YAG laser at 266 nm; comparison with 532 and 1064 nm pulses

Interaction of Nd:YAG laser, operating at 266 nm wavelength and a pulse duration of 40 ps, with AISI 1045 steel was studied. Surface damage threshold was estimated to be 0.14 J/cm². The steel surface modification was studied at the laser fluence of ∼1.0 J/cm². The energy absorbed from Nd:YAG laser beam is partially converted to thermal energy, which generates a series of effects, such as melting, vaporization of the molten material, shock waves, etc. The following AISI 1045 steel surface morphological changes and processes were observed: (i) intensive damage of the target in the central zone of irradiated area; (ii) appearance of periodic surface structures at nano-level, with periodicity in agreement with the used wavelength; (iii) reduction of oxygen concentration in irradiated area; and (iv) development of plasma in front of the target. Generally, interaction of laser beam with AISI 1045 steel (at 266 nm) results in a near-instantaneous creation of damage, meaning that large steel surfaces can be modified in short times.     

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 modifications of AISI 1045 steel created by high intensity 1064 and 532 nm picosecond Nd:YAG laser pulses

Interaction of Nd:YAG laser, operating at 1064 or 532 nm wavelength and a pulse duration of 40 ps, with AISI 1045 steel was studied. Surface damage thresholds were estimated to be 0.30 and 0.16 J/cm² at the wavelengths of 1064 and 532 nm, respectively. The steel surface modification was studied at the laser energy density of 10.3 J/cm² (at 1064 nm) and 5.4 J/cm² (at 532 nm). The energy absorbed from Nd:YAG laser beam is partially converted to thermal energy, which generates a series of effects, such as melting, vaporization of the molten material, shock waves, etc. The following AISI 1045 steel surface morphological changes and processes were observed: (i) both laser wavelengths cause damage of the steel in the central zone of irradiated area; (ii) appearance of a hydrodynamic feature in the form of resolidified droplets of the material in the surrounding outer zone with 1064 nm laser wavelength; (iii) appearance of periodic surface structures, at micro- and nano-level, with the 532 nm wavelength and, (iv) development of plasma in front of the target. Generally, interaction of laser beam with the AISI 1045 steel (at 1064 and 532 nm) results in a near-instantaneous creation of damage, meaning that large steel surfaces can be processed in short time.     

Surface modification of the titanium implant using TEA CO2 laser pulses in controllable gas atmospheres - Comparative study

Interaction of a TEA CO₂ laser, operating at 10.6 μm wavelength and pulse duration of 100 ns (FWHM), with a titanium implant in various gas atmospheres was studied. The Ti implant surface modification was typically studied at the moderate laser beam energy density/fluence of 28 J/cm² in the surrounding of air, N₂, O₂ or He. The energy absorbed from the TEA CO₂ laser beam is partially converted to thermal energy, which generates a series of effects, such as melting, vaporization of the molten material, shock waves, etc. The following titanium implant surface changes and phenomena were observed, depending on the gas used: (i) creation of cone-like surface structures in the atmospheres of air, N₂ and O₂, and dominant micro-holes/pores in He ambient; (ii) hydrodynamic features, most prominent in air; (iii) formation of titanium nitride and titanium oxide layers, and (iv) occurrence of plasma in front of the implant. It can be concluded from this study that the reported laser fluence and gas ambiences can effectively be applied for enhancing the titanium implant roughness and creation of titanium oxides and nitrides on the strictly localized surface area. The appearance of plasma in front of the implants indicates relatively high temperatures created above the surface. This offers a sterilizing effect, facilitating contaminant-free conditions.