The effect of post-grinding heat treatment of alumina and Ag-Cu-Ti braze preform thickness on the microstructure and mechanical properties of alumina-to-alumina brazed joints

Abstract

Copyright © The Author(s). Alumina-to-alumina-brazed joints were formed using 96.0 and 99.7 wt.% Al2O3 and TICUSIL (68.8Ag-26.7Cu-4.5Ti wt.%) preforms of different thicknesses. Brazing was conducted in a vacuum of 131025 mbar at 850 C for 10 minutes. Joint strengths were evaluated using four-point bend testing and were compared to flexural strengths of standard test bars. Post-grinding heat treatment, performed at 1550 C for 1 hour, did not affect the average surface roughness or grain size of either grades of alumina but affected their average flexural strengths with a small increase for 96.0 wt.% Al2O3 and a small decrease for 99.7 wt.% Al2O3. As the TICUSIL preform thickness was increased from 50 to 100 lm, the average strengths of both 96.0 and 99.7 wt.% Al2O3 brazed joints improved. Joints made using 100-lm-thick TICUSIL preforms predominantly consisted of Cu-Ti phases which formed due to excess Ti in the interlayers and non-uniform Ag-rich outflow. Brazed joints of 96.0 wt.% Al2O3 made using 100-lm-thick TICUSIL preforms achieved an average joint strength of 238 MPa with consistent failure in the ceramic.