A Mossbauer spectroscopy study of Ti-Fe interfaces produced by the PVD process

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 Are Bond Sputtering process (ABS(TM)), which uses a combined steered are 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 Mossbauer spectroscopy (GEMS) to study the phase formations in the near surface region of mild steel substrates after various Ti ion etch pre-treatments using the steered are discharge within the ABS process. The work has also investigated a second method using a Balzers BAI640R coating unit. Appropriate enrichment using the Mossbauer isotope Fe-57 has been used, enhancing the interfacial sensitivity of the GEMS technique to detect and identify phases formed by various ion etch processes. The results for the ABS pretreatments 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 pretreated and coated in the Balzers process show some evidence of the FeTi amorphous phase and the development of an iron carbonitride, often identified as epsilon - Fe2-3(CN). (C) 1997 Elsevier Science S.A.