Joining of bulk refractory ceramics: interactions, wetting and interfacial structures.

In the framework of an extensive study aimed at evaluating the wettability and the interfacial characteristics of different metal-ceramic systems for joining, the behaviour of ZrB2 in contact with liquid Ag and its alloys (Cu, Ti, Zr) has been studied. ZrB2 specimens, sintered pure or with different sintering aids by HIP have been used. The wetting and joining experiments have been performed by the sessile drop technique under controlled atmospheres. Contact angles and drop dimensions have been measured by using an in-house developed procedure (ASTRA©) allowing these data to be recorded in real time. Joining tests have also been made with the Ti-Al-V alloy. The dependence of the wetting characteristics and the interfacial reactions have been reported as a function of time, compositions of the ceramic and of the alloy involved. Interfacial structures and reaction products in both specimens resulting from wetting tests and joining processes have been analysed by SEM, EDS, XRD and microindentation tests. In some specimens the interfacial morphologies show the presence of interfacial reaction layers and of different bulk phases which are interpreted in terms of the relevant phase-diagrams and with respect to the final characteristics of the joint.