TEA CO 2 laser surface modification of titanium ceramic thin films

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.