Interfacial microstructure evolution and mechanical properties of Al2O3/Al2O3 joints brazed with Ti–Ni–Nb filler metal.

Herein, prepared Ti40–Ni40–Nb20 (at. %) alloy was utilized as a filler metal to join Al2O3 ceramic. The effect of brazing temperature and holding time on the interfacial microstructure evolution and shear strength of joints were analyzed systematically. The results demonstrated that AlNi2Ti, Ni6Nb7 and layered Ni2Ti4O formed adjacent to Al2O3 ceramic. The microstructure of Al2O3 joint brazed at 1200 °C for 10 min was Al2O3/AlNi2Ti + Ni6Nb7 + Ni2Ti4O/Ti2Ni/TiNi + Nb solid solution (Nbss) eutectic + (Ti,Nb)2Ni/Ti2Ni/Ni2Ti4O + Ni6Nb7 + AlNi2Ti/Al2O3. As brazing temperature or holding time raised, the Ni2Ti4O layer nearby Al2O3 ceramic, AlNi2Ti and Ni6Nb7 developed tremendously whereas TiNi + Nbss eutectic structure gradually increased and tended to coarsen. Eventually, the TiNi + Nbss eutectic structure and (Ti,Nb)2Ni in brazing seam were replaced gradually by bulk Ni6Nb7 because of the depleted Ti element. The shear strength of joints was first increased and then decreased with the increasing of the temperature/holding time. The Al2O3/Al2O3 joints brazed at 1200 °C for 10 min received the maximum shear strength of 93.2 MPa, and the joints fractured primarily at the brazing seam/Al2O3 interface.