Temperature-dependent transformation from whisker- to nanoparticle-strengthened composite interface in the Al₂O₃/Ag-based alloy system and mechanical properties of the joints

Al₄B₂O₉-whisker-coated Al₂O₃ ceramics were bonded by AgCu–4.5 wt.%Ti alloy in vacuum. The microstructure of the whisker-coated Al₂O₃ joints was investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. A continuous (Cu,Al)₃Ti₃O layer formed against the alloy at lower bonding temperatures, and a complex transition zone bordering the whiskers was observed, which consisted of Ag nanoparticles, titanium oxides, TiB₂, (Cu,Al)₃Ti₃O nanoparticles and possible Ag₃Al. As the bonding temperature increased, the Al₂O₃/AgCuTi interface was found to transform from whisker- to nanoparticle-strengthened composite region. Bend test results revealed that both the whiskers grown on Al₂O₃ and the dispersive nanoscale products in the alloy played positive roles in improving the joint properties. The maximum bend strength of the whisker-coated Al₂O₃ joints was 313 MPa at the bonding temperature of 820 °C. - Highlights: • Al₄B₂O₉-whisker-coated Al₂O₃ ceramics were bonded by AgCu–4.5 wt.%Ti alloy in vacuum. • Microstructures of whisker-coated Al₂O₃ joints were investigated in detail. • Both whiskers and the dispersive nanoscale products can improve the joint properties. • The maximum bend strength of the whisker-coated Al₂O₃ joints was 313 MPa.