Surface segregation phenomena encountered during solid carbon active screen plasma nitrocarburizing of AISI 316L

• Published in: Surface & coatings technology 2024-08, Vol.489, p.131091, Article 131091
• Main Authors: Manova, D., Mändl, S., Biermann, H., Dalke, A.
• Format: Article
• Language: English
• Subjects: Active screen; Expanded austenite; Nitrocarburizing; Solid carbon precursor; Stainless steel; Surface particles
• ISSN: 0257-8972
• DOI: 10.1016/j.surfcoat.2024.131091

Plasma nitrocarburizing of an austenitic stainless steel AISI 316L was performed in an N2-H2 atmosphere (50 % H2 and 50 % N2) with a carbon-fiber reinforced carbon (CFC) active screen. The experimental concept of a plasma-discharged CFC active screen in conjunction with a substrate holder at floating potential ensures that no charged particles are present on the sample surface and no sputtering occurs. As a result, carbon contaminations are formed on the surface which were studied in detail with a combination of scanning electron microscopy (SEM) and secondary ion mass spectrometry (SIMS). The results indicate that a layer of about 25–50 nm of carbon is formed. At the same time, a strong segregation of Mn, Ni and Cr is observed below the coating within the steel substrate. Both effects progress with treatment time and there exists a clear correlation between the formation of the carbon layer and the segregation effect. •Unusual surface morphology on AISI 316L for afterglow-plasma nitrocarburizing•Closed carbon film consisting of nanoparticles with a size of 50–250 nm on surface•Strong segregation effects of Mn, Cr and Ni in the near surface region•Surface segregation observed with time delay indicating thermodynamically activation