Wettability and Interfacial Reaction between Alumina and Cu-Based Alloys

In PTLP (partial transient liquid-phase) bonding, the transient liquid phase is sandwiched between a ceramic and a refractory core metal. A transient liquid phase chemistry that reduces the contact angle on the ceramic is necessary to improve strength characteristics. In this study, the effect of additions on the wetting characteristics of liquid Cu on an alumina substrate has been studied in parallel with the study of the joining of alumina through the use of microdesigned multilayer Cu/80Ni·20Cr/Cu interlayers. While Ni additions do not reduce the contact angle of liquid Cu on an Al₂O₃ substrate, additions of 80Ni·20Cr or Cr alone do reduce the contact angle. The contact angle reduction depends upon the Cr content of the sessile drop. The average strength and the standard deviation of PTLP bonded alumina were 259 ± 25 MPa for 99.5% Al₂O₃ and 494 ± 61 MPa for 99.9% Al₂O₃, respectively. The resulting joints can exhibit a high bend strength at room temperature, strengths approaching those of the unbonded alumina, and a relatively narrow strength distribution. In both cases, failure occurred either entirely within the ceramic or primarily in the ceramic, with limited crack propagation along the alumina/interlayer interface.