A Mössbauer spectroscopy study of Ti–Fe interfaces produced by the PVD process

Abstract

The deposition of hard coatings of the type TiC/N on steels enhances the surface properties of the coated substrate. Steel substrates have been pre-heated by the Arc Bond Sputtering process (ABS™), which uses a combined steered arc and unbalanced magnetron arrangement. A critical stage of the ABS process is the titanium ion etch which improves the adhesion of the TiN coating to the substrate. This work uses conversion electron Mössbauer spectroscopy (CEMS) to study the phase formations in the near surface region of mild steel substrates after various Ti ion etch pre-treatments using the steered arc discharge within the ABS process. The work has also investigated a second method using a Balzers BAI 640R coating unit. Appropriate enrichment using the Mössbauer isotope 57Fe has been used, enhancing the interfacial sensitivity of the CEMS technique to detect and identify phases formed by various ion etch processes. The results for the ABS pre-treatments indicate that oxides and carbonitrides that may be formed during the initial stages of the Ti ion etch, are removed after a longer etch. For a conventional 10-min Ti ion pre-treatment a significant formation of both a crystalline FeTi and a Te-rich amorphous phase occurs. The existence of the crystalline phase has also been confirmed by X-ray diffraction. For comparison, samples that had been pre-treated and coated in the Balzers process show some evidence of the FeTi amorphous phase and the development of an iron carbonitride, often identified as ϵ−Fe 2–3(CN).