Interfacial Oxidation Kinetics and Bonding Mechanisms in Reused Co–Cr Alloys for Metal–Ceramic Interfaces

• Interfacial oxidation kinetics of reused Co–Cr alloys were systematically quantified under controlled thermal conditions. • Duplex oxide scales consisting of inner Cr 2 O 3 and outer CoO/CoCr 2 O 4 layers were identified using SEM/EDS and XRD. • Oxide growth followed near-linear kinetics, with whisker-like spinel structures forming at higher temperatures. • Bonding strength was inversely correlated with oxide thickness, confirming the critical role of interfacial scale control. • Optimal adhesion (∼39 MPa) occurred for a thin (∼1.3 µm) chromia layer formed at 790°C for 30 s for reused alloy. • The results provide surface-engineering insights into tailoring oxide films for enhanced metal–ceramic bonding in multi-material systems. Controlling oxide formation at metal–ceramic interfaces is essential for achieving reliable adhesion and long-term stability in multi-material systems. This study investigates the interfacial oxidation kinetics, oxide-layer evolution, and bonding mechanisms of reused cobalt–chromium (Co–Cr) alloys subjected to controlled oxidation heat treatments (OHTs) at 790–980°C for 30–180 s. Oxidation behavior was evaluated through mass-gain kinetics, surface morphology, and phase analysis using SEM/EDS and XRD. The oxide-scale evolution followed near-linear kinetics dominated by Cr 2 O 3 formation at early stages, transitioning to CoO and CoCr 2 O 4 spinel whisker growth with increasing temperature and duration. Cross-sectional analysis revealed a duplex oxide structure—an inner dense chromia barrier and an outer cobalt-rich spinel layer—whose thickness strongly influenced interfacial adhesion. Mechanical testing using the ISO 9693 three-point bending method demonstrated an inverse correlation between oxide thickness and metal–ceramic bond strength, with optimal adhesion (≈ 39 MPa) achieved at 790°C × 30 s for reused alloy. These results elucidate the process–structure–property relationships governing oxidation and interfacial adhesion in Co–Cr alloys, providing mechanistic insight for oxide-layer engineering in high-temperature bonding, coating, and dental applications.