Wettability of transparent YAG (Y3Al5O12) by molten Ag-Cu-Ti alloys

The wetting of transparent YAG (Y3Al5O12) by alloys of the AgCuTi system has been studied for the first time. The role of the activity of Ti in determining the interactions between the brazing alloys and the YAG substrate has been analyzed by CALPHAD method. The low contact angle values ensure very good (at 950°C) and fair (at 850°C and 820°C) wettability conditions. A significant reactivity occurred at the solid-liquid interfaces, with the formation of new phases. TiY2O5 was found at Ag-Ti/YAG interfaces, while a second layer, identified as "M4X", associated to the significant wettability improvement, was specifically found only in the AgCuTi/YAG samples tested at 950°C. All these phases were identified by the newly calculated Ag-Cu-Ti phase diagram and were confirmed by SEM and EDS analyses. The obtained good wettability and the maintained transparency of the YAG are promising for the production of brazed optical windows to be used under extreme conditions.