PNNL

Abstract

The effect of braze interlayer thickness on the strength of alumina brazed with silver-copper oxide reactive air braze (RAB) alloys was evaluated using a four point bend test configuration. The brazed samples had an average fracture strength of 180 MPa or approximately 60 percent of the average monolithic alumina strength. The joint strength values obtained exceeded the yield strength and ultimate tensile strength of the silver interlayer indicating strong ceramic to metal adhesion and the development of a triaxial stress state in the braze interlayer. The average fracture strength was relatively constant (190 ? 60 MPa) in the thickness range of 0.030 mm to 0.230 mm for all test conditions. The braze fracture strength then decreased down to 100 ? 30 MPa as the braze thickness increased from 0.230 mm to 0.430 mm indicating a loss of triaxial constraint with increasing interlayer thickness. In addition, four different fracture modes were observed.