R.Voytovych; "High Temperature Wetting: Application to Brazing of ..."

Faculty of Engineering and Natural Sciences
FENS SEMINARS

High temperature wetting: Application to brazing of alumina by Ti containing alloys

Dr. Raisa Voytovych
CNRS-INP Grenoble, France

Abstract:
High-temperature wetting and adhesion in the soli/liquid systems are of great importance in processing of composites by liquid state routes and in joining of ceramics by brazing alloys. These both parameters can be studied and quantified by sessile drop experiments.
In high vacuum or in neutral or reducing gas atmospheres, most of the metals (Pb, Sn, Ag, Cu, Ni etc.) normally used for brazing metallic parts  do not wet ionocovalent oxides (Al2O3, SiO2, MgO..) and adhere weakly to these solids: the contact angles are much higher than 90° and the adhesion energy represents only a few tens per cent of the cohesion energy of the metal.
Wetting and adhesion of metals on  ceramics can be improved strongly by certain alloying elements forming at the interface, by reaction with the ceramic, continuous layers of new phases. The purpose of the presentation is to describe and discuss the thermodynamics of reactive wetting. The concepts will be illustrated using results obtained for the CuAg-Ti/alumina system. Application of these results to joining of metals to oxides by CuAgTi brazes will be also presented .

April 27th, 2005-13:40, FENS L 047