The effect of cobalt out‐diffusion from the WC‐10%Co/diamond film interface towards the diamond film surface, in terms of carbon phase, chemical composition and dependence of pre‐treatment for enhancement of diamond formation was investigated. Diamond films of various thicknesses were deposited onto substrates pre‐treated by a dual step process consisting of carburization and subsequently diamond seeding or just diamond seeding. Our findings show that the dual step pre‐treatment promotes diamond formation at the initial stages of deposition, decreases the content of out‐diffusing cobalt and prevents self‐delamination after 360 min of diamond film deposition. Conversely, delamination occurs after this deposition time from substrates pre‐treated by seeding only. Under our deposition conditions aggregation of cobalt at the diamond film surface occurs and a nearly constant concentration was measured irrespective of deposition time, along with depletion of cobalt from the diamond film‐substrate near interface region. The composition at the delaminated interface includes a high content of sp2 bonded carbon and a low content of cobalt, which point out that poor adhesion of diamond films to WC‐10%Co is influenced by the out‐diffusion of cobalt and formation of a graphitic interlayer, mainly at the initial stages of diamond film formation.

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