Evaluation of fracture behavior in metal/ceramic joint by acoustic emission

Fracture behavior of Al/sapphire bulk joint fabricated by SAB (surface activated room temperature bonding) was investigated by AE (acoustic emission) method. Direct bonding at atomic level without formation of reaction products restricted the sources of AE generation into interfacial debonding and aluminum fracture itself. In order to reveal the effects of bonding conditions on fracture behavior by non-destructive method, specimens having different bonded area fraction were prepared. The sequential process of interfacial defect growth and propagation of main crack was elucidated by AE source characterization and real time observation of interface through transparent sapphire. Classification of AE signals was carried out by means of source characterization, which well agreed to observed results. While the coalescence of unbonded dominated in Al 2nine(99.5%)-bonded at 40MPa, both coalescence of unbonded and ligament Al fracture resulted in crack propagation in Al 5nine(99.999%)-bonded at 20MPa.