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The diamond thin films chemical vapor deposition (CVD) on sintered tungsten carbide (WC-Co) tools shows increasing interest in the technological research, due to rapid growing utilization of aluminum alloys, like Al-Si alloys, in the automotive industry. Sintered carbides, mainly diamond coated sintered carbides, are very suitable to machine aluminum alloys. The cobalt binder that accounts for the WC-Co substrate toughness degrades the interface film-substrate, catalyzing the formation of graphite preferentially to diamond during the deposition process. In addition, stresses are generated in the interface between WC-Co substrate and deposited diamond film due to thermal expansion mismatch. These two factors are a technological neck to large-scale production of diamond CVD coatings for machining tools. In this work, several interface pre-treatments were developed and applied resulting in high film-substrate adherence, adequate for machining tool purposes.