Secondary Phase Interaction at Interfaces of High-Strength Brazed Joints made using Liquid Phase Sintered Alumina Ceramics and Ag-Cu-Ti Braze Alloys

摘要

Alumina-to-alumina brazed joints were formed using 96.0 and 99.7 wt.% Al2O3 ceramics using 150 µm thick Ticusil^® (68.8Ag-26.7Cu-4.7 wt.% Ti) braze preforms. Brazing was conducted in a vacuum of 1 × 10⁻⁵ mbar at 850 °C for 10 minutes. Joint strengths were evaluated using four-point bend testing and were compared to the monolithic flexural strengths of standard alumina test bars according to ASTM C1161-13. Brazed joints made using 96.0 wt.% Al2O3 consistently outperformed brazed joints made using 99.7 wt.% Al2O3, despite similarities in both the flexural strengths of the standard alumina test bars and the microstructures of brazed joints. Secondary phase interaction led to the formation of Ti5Si3 reaction products at locations where the triple pocket grain boundaries of the 96.0 wt.% Al2O3 surface intersected the Ti-rich reaction layers. It is proposed that due to this interaction, brazed joints made using 96.0 wt.% Al2O3, which were relatively cost-effective to produce, achieved higher strengths than brazed joints made using 99.7 wt.% Al2O3.