Deposition of diamond coatings on Fe-based substrates with Al and Al/AlN interlayers

• High quality diamond was successfully synthesized on SS316 and Kovar with Al and Al/AlN interlayers.
• The Al monolayer and Al/AlN dual layers efficiently suppressed the graphitization and substrate carburization.
• Well adherent diamond coatings were deposited on Kovar substrates.
• The Al/AlN dual layers enhanced the nucleation density and the adhesion of diamond coating.

Because of the carbon diffusion into the substrate and the formation of graphite at the interface, direct deposition of adherent diamond coatings on Fe-based materials is difficult. To address the issue, Al-based interlayers including Al and Al/AlN interlayers were introduced on Fe based substrates (SS316, FeNiCo) to enhance diamond deposition, which was carried out in a microwave plasma chemical vapor deposition (MPCVD) reactor using a CH4–H2 mixture. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, synchrotron-based X-ray absorption spectroscopy (XAS), and indentation testing. The results show that single Al layer can effectively suppress the formation of graphite and the inward diffusion of carbon into the substrate, and thus enhance diamond nucleation and growth. The dual layers of Al/AlN can further enhance the adhesion of diamond coatings comparing to the single Al interlayer.