Vacuum brazing of YSZ ceramic and TC4 alloy with a Ti20Zr20Hf20Cu20Ni20 high entropy amorphous alloy

The joint embrittlement induced by bulky intermetallic compounds (IMCs) formed during brazing greatly impairs the bonding strength of Yttria-stabilized zirconia (YSZ) ceramic and Ti6Al4V (TC4) alloy. To inhibit the growth of IMCs and prevent the formation of bulky phases, in this work, a Ti20Zr20Hf20Cu20Ni20 high-entropy amorphous alloy was innovatively used for brazing YSZ-TC4. The microstructure and mechanical properties of the joint brazed at different temperatures were studied in detail. The results show that the joint is mainly composed of the alpha-Ti solid solution phase and eutectoid microstructure which composites of alpha-Ti matrix and fine acicular (Ti, Zr, Hf)2(Cu, Ni) second phase. Through thermodynamic calculation, it was determined that the synergistic interaction of multi-principal elements significantly increased the mixing entropy of the joint and hence facilitated the formation of solid solution phases, inhibiting the formation of bulky IMCs. The maximum shear strength of the joint can be reached 240.5 MPa with the brazing parameters of 960 C and 10 min, which was much higher than most of the commonly used Ag-Cu or Ti-based filler metal. This research proves that using high entropy amorphous alloy as filler metal is a promising method to reduce the formation of intermetallic compounds in the interfacial microstructure of brazed joints.