Interfacial microstructure and mechanical properties of Al₂O₃ ceramics and TC4 alloys brazed with Cu foils

A successful brazing connection between Al₂O₃ ceramic and TC4 alloy was achieved using Cu foil, producing well-formed joints without obvious defects such as cracks. The effects of brazing temperature and holding time on the microstructure and mechanical properties of Al₂O₃/TC4 joints were systematically investigated, revealing the joint formation mechanism. The results show that the typical interfacial microstructure of Al₂O₃/TC4 joints brazed at 910 ℃ for 10 min is Al₂O₃/Ti₃(Cu,Al)₃O /AlCu₂Ti + (Ti,V)₂(Cu,Al) + Ti(Cu,Al) + Ti₃Cu₄/α-Ti + β-Ti + Ti₂Cu/TC4. With increasing brazing temperature, the Ti₃(Cu,Al)₃O reaction layer first gradually thickens and then remains stable. Due to the gradual overflow of liquid metallic compounds at high temperatures, the overall joint width shows a decreasing trend, while Ti₃Cu₄ forms continuous layers. The shear strength of the joints first increases and then decreases. With prolonged holding time, the joint width gradually decreases and the thickness of Ti₃(Cu,Al)₃O reaction layer increases. The excessively thick reaction layer adversely affects the mechanical properties, causing the shear strength to first increase and then decrease, reaching a maximum value of 102 MPa at 910 ℃ after 10 min holding time.