Growth of PVD-AlTiN film on Co-based alloy: Preferred orientation and adaptively formed transition layers

To achieve a better understanding of the interaction between the film and the ductile Co-based binder phase in cemented carbide substrate and the associated interface microstructure evolution, a model alloy of 85.1Co–9.2W–4.7Cr3C2–1.0VC was prepared. Ti0.94Si0.06N/TiAlSiN/Al0.52Ti0.48N coating was deposited on the Co-based alloy by a DC magnetron sputtering technique. High-resolution transmission electron microscopy observation and high-resolution energy dispersion spectrum analysis reveal a complex film-substrate structure. An interface-centered bilateral transition layer, i.e., nanocrystalline AlTiN and hcp-Co, and double sub-transition layers, i.e., bcc-W and disordered arrangement of Co atoms are identified. The formation mechanisms for the sub-transition and transition layer are discussed. Based on the AlTiN transition layer phenomenon, the reason for the substantial texture coefficient TC(111) difference between fcc-AlTiN and fcc-TiSiN (5.9/3.6 vs. 2.9) is discussed. Considering the significance of the observed semi-coherent relationship for the bcc-W/AlTiN interface and the positive adaptability of cobalt, suggestions are proposed for the composition design of cemented carbide substrate and the film deposition rate controlling.