Investigation of the modes of thin metal and ceramic films (0,3-1 μm) removal from the glass and stainless steel substrate by IR and UV laser radiation has been performed. It is presented that the efficient film destruction and removal occurs due to laser induced thermal strength under laser fluxes of ~0.5 J/cm2 not sufficient for phase transformation.
The surface modification of titanium based ceramics thin films, induced by pulsed laser beam, was investigated in this work. Thin films of titanium nitride (TiN) and titanium diboride (TiB2) were deposited on austenitic stainless steel substrate by two Physical Vapor Deposition (PVD) techniques and exposed in air atmosphere to a focused Transversely Excited Atmosphere (TEA) CO2 laser irradiation. In these experiments two types of laser pulses have been used. One pulse was composed of an initial spike (FWHM equals 120 ns) with a tail (duration of 2 microseconds) while the other contained only the initial spike (FWHM equals 80 ns). Morphological changes of deposited ceramics, induced by successive laser pulses, have shown a dependence on the laser beam parameters (pulse energy, laser pulse duration, peak power density, number of pulses, etc.) and thin films characteristics. Thin films, investigated in this work, possessed reflectivity above 90% at wavelength of about 10 microns. Pulse peak power densities of 100 and 170 MW/cm2 were used in these experiments and have induced the surface modifications of TiN and TiB2 thin films. Depending on laser beam parameters, a change of color, grain growth, hydrodynamic effects, in TiN thin film were registered while on TiB2 we noticed a change in color of the thin film, cracking and exfoliation.
An efficient small scale TEA (Transversely Excited Atmospheric) CO2 laser has been considered. The laser was a low flowing, UV preionized, pulsed system. Specific design of the head as well as the electrical circuit ensure the laser operation with high efficiency and reliability. Nonconventional CO2/Y, Y equals N2/H2; H2/He and H2 gas mixtures showed relatively high energy output. CO2/N2/H2 mixture as the most superior one produces output energy and peak power of 220 mJ and 1.40 MW, respectively. High-energy output of the laser was employed for surface modification of austenitic stainless steel AISI 316 and titanium nitride (TiN) coating deposited on the same steel substrate. Used laser peak power densities of 100 and 170 MW/cm2 have induced the morphology changes of AISI 316 steel and TiN coating, respectively.
The interaction of a Transversely Excited Atmospheric (TEA) CO2 laser, pulse duration less than 100 ns, with austenitic stainless steel-AISI 316 and low thickness coating of titanium-nitride (TiN) deposited on steel are considered. The results have shown that steel as well as coating had been modified by TEA CO2 laser beam. Compared to steel, TiN have shown more diverse changes in the bombarded area: crater like form, solidified boundary and droplets. On austenitic stainless steel--wall material of the vacuum vessel for a fusion reactor--different mechanism of surface degradation was found. A qualitative description comprises: surface corrugation, cracking and resolidified.
The interaction of a Transversely Excited Atmospheric (TEA) CO2 laser, pulse duration less than 2 µs, with low thickness coatings of titanium-nitride (TiN) and titanium-aluminum-nitride (TiAl)N, deposited on steel-substrate is considered. The investigations have shown that both coatings had been intensively modified by TEA CO2 laser beam. The (Ti,Al)N compared to TiN shows more expressed changes in the bombarded area: cracking and other surface modifications. Intensive surface exfoliation was observed only for (Ti,Al)N. Especially attention was devoted to the effects of laser pulse shape on morphology features. Generally, laser pulses with tail induced more signified changes on the coating surface.
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