Interfacial Microstructure Evolution and Mechanical Properties of TC4/MgAl₂O₄ Joints Brazed with Ti–Zr–Cu–Ni Filler Metal

In the present study, Ti–Zr–Cu–Ni amorphous filler metal was used to braze MgAl₂O₄ ceramic and Ti–6Al–4V (TC4) at 875, 900, 925, 950, 975 and 1000 °C for 10 min. The effects of brazing temperature on interfacial microstructure and mechanical properties of the joints were analyzed. The results showed that typical microstructure of the TC4/MgAl₂O₄ joint was solid solution (SS) α-Ti, acicular α-Ti + (Ti, Zr)₂(Ni, Cu) layer, metallic glasses and TiO. With the increase in brazing temperature, (Ti, Zr)₂(Ni, Cu) layer gradually dispersed at bonding interface, a continuous layer of TiO appears near MgAl₂O₄ ceramic. With the increase in brazing temperature, the hard and brittle (Ti, Zr)₂(Ni, Cu) layer gradually dispersed, resulting in the maximum shear strength of 39.5 MPa. The high-resolution TEM revealed the presence of amorphous structure, which is composed of Ti, Zr, Cu, Ni and Al. The values of δ and ΔH_mix are calculated to be about 8% and −39.82 kJ/mol for the amorphous phase.