Executive Summary : | Diamond, the hardest known material, is not suitable for fabricating machining tools due to its poor chip resistance. However, cemented tungsten carbide (WC-Co) has high fracture toughness and is commonly used for manufacturing machining tools. By depositing a thin layer of CVD diamond coating on WC-Co substrate, the hardness of diamond can be combined with WC-Co's toughness. However, poor adhesion leads to a lesser lifetime for the diamond-coated tools. Realizing adherent diamond coatings on WC-Co substrates has always been a challenge, as it requires eliminating carbon-cobalt interactions during the diamond deposition process. The conventional chemical etching method is not feasible for high cobalt content WC-Co substrates. The current industrial trend is to increase cobalt content above 8% to improve the toughness of machining tools. The proposed research aims to develop novel, graded layer diamond coatings, along with a CrN interlayer, to realize adherent diamond coatings on high cobalt content WC-10%Co inserts for machining applications. The CrN layer acts as a diffusion barrier, providing improved chemical and mechanical adhesion to both diamond films and WC-Co substrates. Adopting a graded NCD/MCD coating methodology will exploit the advantages of both MCD and NCD layers, improving adhesion. The potential of diamond-coated WC-10%Co inserts with a CrN interlayer will be demonstrated by machining Al-si alloy and comparing results with commercially available hard coating tools. This research has significant economic impact, as the global hard coatings market is valued at 1 billion UsD and projected to reach 1.4 billion UsD by 2026. |