Microstructure of reactive magnetron sputtered S-phase coatings with a diffusion sub-layer

The main objective of the work was to investigate the microstructure of S-phase coatings obtained by reactive magnetron sputtering at different temperatures and with various nitrogen concentrations in the working atmosphere. Particular attention was paid to the formation of a diffusion sub-layer in the austenitic substrate. The coatings were deposited on austenitic stainless steel substrates in an argon-nitrogen gas mixture. Three different nitrogen concentrations in the working gas were used in the experiments (15, 33 and 50 vol.%), and five substrate temperatures (200, 250, 300, 350 and 400 °C). The phase composition was evaluated using X-ray diffraction (XRD). X-ray microanalysis (WDS) and glow discharge emission spectroscopy (GDOES) techniques were used to study the nitrogen content and distribution in the coatings. The microstructure was investigated using a scanning electron microscope (SEM). Formation of the S-phase diffusion sub-layers was observed in the atmospheres containing 50 and 33 vol.% N2 respectively at temperatures of 300 and 350 °C or higher. Nitrogen diffusion into the substrate also occurred with the 15 vol% N2 atmosphere at 350 °C or higher although no supersaturated solution was formed in these conditions.