Interfacial microstructure and mechanical properties of the TiC-Ni cermet/Ag-Cu-Zn/Invar joint

Abstract

TiC-Ni cermet and Invar was brazed with Ag-Cu-Zn alloy in vacuum and the interfacial microstructure and mechanical properties were studied. The interfacial microstructure of the joint brazed at 910 °C for 10 min was TiC-Ni cermet/(Ag) + (Cu, Ni) + TiC/(Cu, Ni) + (Ag)/(Cu, Ni)/(Cu, Ni) + (Fe, Ni)/Invar alloy. When the temperature increased from 740 °C to 940 °C, (Cu, Ni) reactive layer at the cermet side dissolved into the brazing seam and became discontinuous. Moreover, TiC particles presented gradient distribution in the reactive region of the joint brazed between 850 °C and 940 °C. Meanwhile, the amount of (Cu, Ni) detaching from the cermet and entering the brazing seam increased. The shear strength firstly increased and then sharply decreased with temperature. The maximum shear strength of 161 MPa was obtained at 910 °C for 10 min and the joint was fractured on (Ag). The change trend of the shear strength between 820 °C and 940 °C was attributed to the increase thickness of the functional gradient material layer in the reactive region and the decrease of the (Cu, Ni) amount in the penetration region and the reactive region with the temperature increase.