ABSTRACT
This work presents preliminary results regarding improving the mechanical, wear and protective properties (hardness, coefficient of friction, corrosion resistance) of AISI 304 stainless steel surfaces by open atmosphere cold plasma surface treatment method. Comparative evaluations of the morphological, corrosion resistance, mechanical and tribological properties for different periods of treatment (using N2 gas for cold plasma generation in an open atmosphere) were performed. AFM surface analyses have shown significant surface morphology modifications (average roughness, FWHM, surface skewness and kurtosis coefficient) of the treated samples. An improved corrosion resistance of the N2 treated surfaces in open atmosphere cold plasma could be observed using electrochemical corrosion tests. The mechanical tests have shown that the surface hardness (obtained by instrumented indentation) is higher for the 304 stainless steel samples than it is for the un-treated surface, and it decreases gradually for higher penetration depths. The kinetic coefficient of friction (obtained by ball-on-disk wear tests) is significantly lower for the treated samples and increases gradually to the value of the un-treated surface. The low friction regime length is dependent on the surface treatment period, with a longer cold plasma nitriding process leading to a significantly better wear behavior.
ABSTRACT
Mixtures of nitrogen-doped titanium dioxide (TiO2:N) with different concentrations of Ag and/or SiO2 particles (0.5, 1 and 2 wt.%) were prepared in solid state by mechanico-chemical interactions. Using UV-VIS spectroscopy, Raman scattering, photoluminescence (PL) and photoluminescence excitation (PLE), the influence of the particles on the host material is evaluated. UV-VIS spectroscopy studies indicate a TiO2:N band gap shift to the UV range with increasing concentrations of SiO2 and Ag particles. PL intensities decrease with increasing concentrations of Ag and/or SiO2 particles in the TiO2:N host matrix, which in turn could effectively restrict the electron and hole recombination. To explain these processes, the different de-excitation ways will be advanced, taking into account the energy levels diagram of TiO2:N/Ag, TiO2:N/SiO2 and TiO2:N/Ag/SiO2 systems. PLE spectra show a gradual decrease in their relative intensities after 165 min of continuous irradiation due to photosensitivity of TiO2:N. The plasmonic effect of Ag particles in the TiO2:N/Ag system is highlighted for the first time by PLE studies.