The Thermal Relaxation Effect in The Bending Joints Between Metal and Alumina With A Modified Macrogeometry of The Alumina Surface To Be Joined.

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The effect of a modified macrogeometry of alumina surface to be joined on the performance of Alumina / Metal joints was investigated. High strength alumina with various surface macrogeometry were prepared by centrifugal net-shape compacting process, and were joined with SUS304 stainless steel, KOVAR and HT80 using Ag-27.5mass%Cu-2.0mass%Ti brazing filler metal at 1113 K for 0.6 ks. The microstructure and reaction layer of the joints were investigated by SEM and EDX. The thermal stresses around the joints were calculated by FEM analysis and the reduction of critical stress by changing surface macrogeometry of alumina were estimated.The results of the study obtained are as follows.1. In the case of plane macrogeometry of alurnina, alumina can be joined to KOVAR and HT80 without cracks, whereas many cracks observed in alumina / SUS304 joint.2. Three phases are commonly observed at the boundary of each joint regardless of metal types. Those are Ti rich layer, Ag-Cu eutectic, and a intermetallic phase (CuィイD23ィエD2Ti, AlTi, or AlィイD23ィエD2Ti).3. Alumina / KOVAR joint shows four-point bending strength of 270 MPa. The crack propagates in Ti rich layer, that is, the whole strength of the joint is determined principally by the strength of the Ti rich layer.4. FEM thermal stresses analyses show that surface macrogeometry of alumina has no positive effect on alumina / KOVAR joint, but it reduces the stress of 20 MPa on alumina / SUS304 joint. The alumina / SUS304 joints with variovs surface macrogeometry of alumina, however, show some cracks. It is considered that the quantity of stress relaxation is not sufficient for alumina / SUS304 joint.