Transient liquid phase bonding of alumina to alumina via boron oxide interlayer

Alumina bulks coated with 3 μm boron oxide layer were bonded at various temperatures and times in air. The joining strength, interfacial compounds and morphologies of cross-sections and fracture surfaces were investigated by means of four-point bending, X-ray diffraction and scanning electron microscopy. The maximum bending strength is 71 MPa for alumina bonded at 800 °C for 15 h. The layered metastable phase of 3Al2O3B3O3 forms at the beginning of joining at temperature above 700 °C. This interlayer transforms into a whisker structure consisting of 2Al2O3B3O3 and 9Al2O32B3O3 with increasing temperature and time. Models for the growth and morphology of these interfacial compounds are proposed.