Study on Reactive Air Brazing of p-SiO₂ Ceramic with Ag-xCuO Filler Metal

Abstract

Reactive air brazing of porous SiO2 ceramic (p-SiO2) was achieved using Ag-CuO filler metal. When brazing p-SiO2, two main problems existed. Firstly, the wettability of the Ag filler metal on the surface of p-SiO2 was poor. Secondly, the residual stress caused by the mismatch of the coefficient of thermal expansion was high in the joint. In order to solve these problems, the effects of CuO contents on the p-SiO2 brazed joint were analyzed. In a wetting experiment, the addition of CuO significantly improved the wettability of the Ag-CuO/p-SiO2 system. With the content of CuO increasing, the contact angle decreased from 90° to 0°. In addition, when the content of CuO increased to 0.5 mol%, the contact angle decreased from 90° to 52°. Then, during brazing p-SiO2 with the Ag-xCuO filler metal, the typical interfacial microstructure of the joints brazed at 1000 °C for 30 min was p-SiO2 ceramic/Ag (s,s) + SiO2 + CuO/Ag (s,s)/Ag (s,s) + SiO2 + CuO/p-SiO2 ceramic. Meanwhile, Ag-CuO infiltrated into the p-SiO2 ceramic and an infiltration layer formed. The infiltration layer was composed of Ag (s,s) + SiO2 + CuO and the infiltration layer was conductive to form a good gradient transition of the coefficient of thermal expansion (CTE). Then, the residual stress in the joint was released and the shear strength improved. In addition, with the content of CuO increasing, the depth of the infiltration layer increased. Furthermore, when the content of CuO was 0.5 mol%, the maximum shear strength of the joint was 55 MPa.

Keywords

• reactive air brazing
• Ag-CuO
• wettability
• infiltration layer
• residual stress