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 10 min 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.