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

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 th e near surface region in a pre-treatment step prior to deposition of e.g. d iamond films. The removal of the Go-binder phase by etching may weaken the near surface region resulting in a decrease of performance of the coated ce mented carbide tool. An alternative to the selective etching of the cobalt binder phase could be the formation of chemically inactive Co containing in termetallic phases. The present paper focuses on the formation of intermeta llic BCo and AlCo phases in the near surface region of pure Co substrates a nd cemented carbide insert tips. One method investigated was to coat the su bstrates with B and Al by PVD with subsequent tempering. Another method tes ted was powder pack cementation. Phase analyses were performed by grazing i ncidence X-ray diffraction. The suitability of the pre-treatment methods fo r the CVD deposition of diamond films on cemented carbide insert tips was i nvestigated by WDX linescans and element mappings, SEM, AES point measureme nts, and wear tests. The analyses revealed in all cases the formation of in termetallic BCo and AlCo phases after boronizing and aluminizing of the sub strates. Especially the boronizing of the substrates by a powder pack cemen tation process led to distinctly enhanced wear resistance of the diamond fi lms. (C) 1999 Elsevier Science S.A. All rights reserved.