Quantum Mechanical Investigation of Adhesion and Interface Stability Between TiN Coating and Cemented Carbide Substrate

This study presents a quantum mechanical investigation of the adhesive bonding and interface stability between TiN hard coating and WC-Co cemented carbide substrate, combining density functional theory calculations with experimental validation to develop mechanistic understanding of coating adhesion failure modes relevant to coated cutting tools used in Nigerian machining operations. TiN-coated cemented carbide tools are widely used in Nigerian machine shops and tool reconditioning facilities, and coating delamination at the tool-substrate interface is the dominant failure mode limiting coating re-use potential. DFT calculations are performed using VASP with the PBE functional on supercell models of the TiN/WC interface with varying interfacial terminations (TiN-termination, TiC interlayer, and direct TiN-Co contact). Work of adhesion, interfacial fracture energy, and charge density distribution are calculated for each interface model. Electronic structure analysis is performed via projected density of states and Bader charge analysis to characterise bonding character. The DFT predictions are correlated with experimental scratch test critical loads and nano-indentation hardness and stiffness measurements on TiN coatings deposited by cathodic arc PVD on WC-Co substrates with and without TiC interlayer. Cross-section TEM with EELS compositional profiling is performed to characterise the experimental interface. Findings confirm that TiC interlayer deposition improves work of adhesion by 42 percent relative to direct TiN-WC contact, consistent with scratch test results. Keywords: DFT, TiN coating, WC-Co substrate, adhesion, interface stability.