Phase interfaces between AlTiN and WC/Mo2C in WC-Mo2C substrate and the related characteristics

To explore the synergistic effect of the hard phase and the ductile binder phase in hardmetal substrate to the coatings, a binderless WC-6Mo2C-0.68Cr3C2-0.37VC (bWC) model alloy and a WC-10Co-0.65Cr3C2-0.35VC reference alloy with similar grain size (~0.4 μm) were used as substrates. Ti0.94Si0.06N/TiAlSiN/Al0.52Ti0.48N coating was deposited by DC magnetron sputtering. Scratch testing (loading range 0-30 N) results show that complete removal of the coating on bWC substrate occurs under a substantially higher critical load LC2 (28.3 N vs. 21.4 N), but accompanied by a quite earlier cohesion failure expressed by LC1 (LC2 − LC1 = 16.4 N vs. 1.0 N). To reveal the reason behind the high adhesion strength, phase interfaces between AlTiN and WC/Mo2C based phase in bWC substrate were investigated by HRTEM. Coherent and semi-coherent epitaxial growth relationships at the AlTiN/WC interfaces and semi-coherent epitaxial growth relationships at the AlTiN/Mo2C interfaces are easily identified. The minimum lattice misfit (1.9%) is observed when AlTiN growths on (0001)WC along its 4¯22¯ direction. The reasons behind the related phenomena are discussed.