Joining mechanism between Al₂O₃-Ag-Cu-Ti composite coating and GCr15 substrate

Using a mixture of Al₂O₃, Ag, Cu, and Ti particles, an Al₂O₃-Ag-Cu-Ti composite coating was fabricated on GCr15 substrate by plasma spraying. To obtain strong joining between the composite coating and substrate, samples were heated at 700-1000°C for 10min in a vacuum chamber. The microstructure and composition of the coating were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). SEM images revealed that the shapes of the Ag and Cu particles in the coating changed because of a eutectic reaction when the joining temperature exceeded 800°C. SEM and XRD results showed that a thin TiC and Ti₂Fe composite layer was formed at or close to the interface when the joining temperature was above 900°C. In addition, an obvious reaction layer with a concentration of elemental Ti between the Ag-Cu-Ti alloy and the Al₂O₃ particle was formed when the joining temperature exceeded 800°C. Evaluation of the mechanical properties of the join between the composite coating and the substrate was performed using an impact tester, and the sample joined at 900°C showed excellent adhesion strength and toughness.