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

Abstract

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 mu m (a-CN = 0.6 and TiAlN = 4.2 mu m). 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 similar to 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 mu m. 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.