Microstructure and Mechanical Properties of a SiO2 Ceramic and TC4 Alloy Joint Brazed with a Nanocomposite Filler

Abstract

Vacuum brazing of TC4 alloy and SiO2 ceramic was achieved using a nano-AgCuNi braze alloy. The melting temperature of nano-AgCu powders was analyzed by differential scanning calorimeter. Furthermore, the effects of the Ni content on the microstructure and mechanical properties of the joints were studied. The results showed that the melting temperature of the nano-AgCu filler was 774 °C. A decrease in the melting temperature of 6 °C was observed, compared with the general AgCu filler, and this decrease enabled the interfacial reaction of the joint to begin earlier. The typical interfacial microstructure of the TC4/nano-AgCuNi/SiO2 ceramic joint brazed at 950 °C for 10 min was TC4/α-Ti + Ti2(Cu,Ni) + Ti2(Ni,Cu) hypereutectoid structure/Ti2(Cu,Ni) compound with α-Ti + Ti2(Cu,Ni) + Ti2(Ni,Cu) hypereutectic structure/Ti4O7 + TiSi2/SiO2 ceramics. The homogeneous microstructure of α-Ti + Ti2(Cu,Ni) + Ti2(Ni,Cu) hypereutectoid structure primarily existed in the diffusion layer. Additionally, the refined α-Ti + Ti2(Cu,Ni) + Ti2(Ni,Cu) hypereutectic structure created via a eutectic reaction and Ti2(Cu,Ni) compound was distributed in the brazing seam. The Ni content could influence the formation of Ti-Cu-Ni ternary intermetallic compounds (IMCs). An increase in Ni led to an increase in the α-Ti + Ti2(Cu,Ni) + Ti2(Ni,Cu) hypereutectic structure in the brazing seam. The shear strength of the brazed joints first increased and then decreased with the increase in the nano-Ni content, and the optimal shear strength of 30.1 MPa was achieved at 10 wt.% Ni. The increase in the α-Ti + Ti2(Cu,Ni) + Ti2(Ni,Cu) hypereutectic structure and the decrease in brittle compounds enhanced the shear strength of the joint. Fracture analysis of the joints brazed at 950 °C for 10 min indicated that the cracks mainly occurred in SiO2 ceramic.