Dual-roughness enhances adhesion in WC-Co coatings under substrate-induced constraints

Adhesive strength is a critical determinant of longevity in coating-substrate systems, particularly under thermal mismatch stresses induced by substrate constraints. This study investigates the adhesion performance of WC-Co coatings on steel substrates with distinct single-scale (mono-roughened) and dual-scale (bi-roughened) interfacial designs under thermal cycling within the temperature range of 0 - 500°C. For instance, at 0°C, mono-roughness of 7.5 μm exhibit an adhesive strength of 58 MPa, while dual roughness having sub-roughness with a tailored angle of 60° elevates this value to over 90 MPa, which is more than 50% improvement. Results demonstrate that the bi-roughened interface significantly outperforms its mono-roughened counterpart, retaining 93% of its baseline adhesion strength at 500°C compared to a 30% reduction in the mono-roughened system. In single-scale roughness (mono-roughening) designs, residual stresses concentrate at free edges and interfacial regions, promoting single dominant crack propagation under thermal loading, particularly at elevated temperatures. For the bi-roughening design, the residual stresses in the interface are reduced dramatically and individual cracks at every bi-roughening step are not connected to each other, which can be responsible for holding high adhesive strength. Importantly, the dual-scale design mitigates stress amplification caused by thermal mismatch during service, enhancing both coating reliability and performance under high-temperature conditions.