Formation of intermetallic cobalt phases in the near surface region of cemented carbides for improved diamond layer deposition

Abstract

Due to the negative influence of cobalt upon a number of CVD processes, the cobalt binder phase in cemented carbide substrates has to be removed in the near surface region in a pre-treatment step prior to deposition of e.g. diamond films. The removal of the Co-binder phase by etching may weaken the near surface region resulting in a decrease of performance of the coated cemented carbide tool. An alternative to the selective etching of the cobalt binder phase could be the formation of chemically inactive Co containing intermetallic phases. The present paper focuses on the formation of intermetallic BCo and AlCo phases in the near surface region of pure Co substrates and cemented carbide insert tips. One method investigated was to coat the substrates with B and Al by PVD with subsequent tempering. Another method tested was powder pack cementation. Phase analyses were performed by grazing incidence X-ray diffraction. The suitability of the pre-treatment methods for the CVD deposition of diamond films on cemented carbide insert tips was investigated by WDX linescans and element mappings, SEM, AES point measurements, and wear tests. The analyses revealed in all cases the formation of intermetallic BCo and AlCo phases after boronizing and aluminizing of the substrates. Especially the boronizing of the substrates by a powder pack cementation process led to distinctly enhanced wear resistance of the diamond films.