In recent years vanadium-doped hard coatings have become available as possible candidates for self-lubrication at high temperatures. Their low coefficient of friction has mainly been attributed to the formation of the V2O5 phase at temperature of about 500°C. However, the formation of vanadium oxides must be controlled by the out-diffusion of vanadium in order to achieve the combination of a low coefficient of friction and good mechanical properties for the protective coatings. In this study a nanolayer CrN/(Cr,V)N hard coating was investigated to see whether it could better control the vanadium out-diffusion. It is based on the idea that the top chromium oxide layer acts as a diffusion barrier to the vanadium ions during the oxidation at elevated temperatures ()500 °C) due to the immiscibility between the vanadium oxides and the chromium oxides. Special attention was given to the oxidation process that takes place at the growth defects.
COBISS.SI-ID: 28907559
The coatings CrN/CrVN were extensively analyzed from the tribological point of view, while for reference we also analyzed the standard monolayer coatings CrN and CrVN. Numerous factors can influence the coating tribological properties. In contrast to most publications which typically use standard lab conditions we put an emphasis on the aspect of the surrounding atmosphere. We performed tribological tests in air (high, medium and low humidity), nitrogen and oxygen environment. To fully understand the processes during tribological testing, the wear mechanisms were investigated for each hard coating separately. We found important differences between results of tribological tests carried out in ordinary air, oxygen (main point is absence of moisture) and nitrogen (main point is absence of oxidation). The lowest wear volume was measured at the above mentioned nanolayer coatings.
COBISS.SI-ID: 28214055
A 4.8 µm thick double layer a-CN/TiAlN coating (a-CN=0.6 and TiAlN=4.2μm) 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/cm2. Laser-induced changes of the surface showed dependence on laser intensity and number of pulses. Irradiations at the highest intensity resulted in preservation of one or both layers up to 10 pulses, while at lower intensity (10^13W/cm2) 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/cm2. 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 (10^14W/cm2) and laser pulse count of ≥50 resulted in the creation of crater like damages with depth up to 20μm. Generation of LIPSS as well as craters can be of great interest for contemporary technologies.
COBISS.SI-ID: 28747559