Analysis of the Reaction Layer Formed during Sapphire-Sapphire Brazing Using a Ag-Cu-Ti Filler Metal for Gas-Pressure Sensors

The present research paper introduces a reliable and economical method for direct brazing using an active Ag-Cu-Ti filler metal that can ensure effective brazing. The sapphire-sapphire brazing process has been conducted at temperatures in the range of 830-900 degrees C for durations in the range of 15-30 min in a high-vacuum (10(-4) Pa) furnace. Material and microstructural characterization involved the use of scanning electron microscope-energy-dispersive system (SEM-EDS) and transmission electron microscope (TEM) for investigating the bonding joint morphologies. Two uniform reaction layers were observed to have formed at the sapphire/brazed area interface. On the sapphire side, the first reaction layer, which was uniform and had a thickness in the range of 0.13-0.17 mu m, was identified as a TiO phase, whereas the second layer was identified as a Cu3Ti3O phase with a thickness in the range of 1.72-2.43 mu m. The uniformity of the Cu3Ti3O phase was found to decrease with increasing brazing temperature and time. Therefore, in this research, a lower brazing temperature and time (830 degrees C/15 min) were chosen so as to avoid bonding degradation.