Microstructure and Shear Strength of Brazing High Entropy TiZrHfNbMo Alloy and Si3N4 Ceramics Joints

The effects of different brazing processes on the interfacial microstructure and shear strength of TiZrHfNbMo high-entropy alloy (HEAS) and Si3N4 ceramic brazed joints were studied. There is no obvious defect in a brazed TiZrHfNbMo HEAS/AgCuTi/Si3N4 ceramic joint, and the two materials have good metallurgical bonding. The typical interface microstructure is Si3N4/Ti5Si3/Ag solid solution +Cu (s,s)+ CuTi/Cu2Ti/Cu4Ti + TiCu(Hf,Zr)NbMo/TiZrHfNbMo HEAs. With the increase of brazing temperature, the dispersed CuTi phase agglomerates in the brazed joint, and acts as the nucleate of the Cu-based solid solution. The thickness of the reaction layer increases with the increase of phases in the reaction layer on both sides of the joint. When the brazing temperature is 800 °C, 820 °C, 840 °C and 860 °C, the shear strength of the brazed joint is 30 MPa, 72 MPa, 86 MPa and 21 MPa, respectively. The formation of CuTi and Ti5Si3 intermetallic compounds increases the thickness of the reaction layer, and improves the strength of the joint. However, excessive CuTi and Ti5Si3 intermetallic compounds lead to a significant decrease in joint strength. The grain coarsening of the joint can also affect the strength of the joint.