Development and characterisation of Ag–Cu–Ti brazes prepared with planar flow casting

Using the technique of rapid quenching from the melt, it becomes possible to prepare active brazes of Ag–Cu–Ti composition with varying silver content for joining alumina ceramics, involving a single technological operation in the form of ribbons up to 40 mm wide and 50–100 μm thick. The melting temperature of the alloys increased with decreasing silver content, in agreement with the phase diagram. The wetting of the alumina by the brazes, determined by the sessile drop method, has been satisfactory for all alloys. The ceramic/ceramic joints attain high joint strengths above 150 MPa. Microchemical and structural investigations of the reaction interlayer (alumina/Ag–Cu–Ti/alumina joint) have been performed using x-ray spectroscopy, EDX analysis and scanning electron microscopy. By transmission electron microscopy and electron diffraction the structures formed in the reaction zone of the joint have been determined. It has been found that the reaction zone near alumina consists of TiO while the zone further from alumina, rich in Ag–Cu, contains mainly the mixture of Ti2O3 and Cu2O.