Lawrence Berkeley National Laboratory

The mechanical properties and microstructural evolution of metal-ceramic bonds produced using a transient liquid phase (TLP) are described. Alumina (Al2O3) was joined at 500 degrees C, 600 degrees C, and 700 degrees C using a multilayer In/Cusil-ABA (R) (commercial copper-silver eutectic brazing alloy)/In interlayer. The introduction of thin In cladding layers allows the system to bond at much lower temperatures than those typically used for brazing with Cusil-ABA (R), thereby protecting temperature-sensitive components. After chemical homogenization, the interlayers retain an operating temperature range similar to that of the brazed joints. TLP bonds made at 500 degrees C, 600 degrees C, and 700 degrees C with holding times ranging from as low as 1.5 h to 24 h had average fracture strengths above 220 MPa. The effects of bonding temperature and time on fracture strength are described. Preliminary analysis of the interlayers shows that the Ag-In or Cu-In intermetallic phases do not form. Considerations unique to systems with two-phase core layers are discussed. Experiments using single-crystal sapphire indicate rapid formation of a reaction layer at 700 degrees C, suggesting the possibility of making strong bonds using lower temperatures and/or shorter processing times.