Study on modification of joining layer structures of ceramic/metal bondings with heat treatment

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To produce ceramic/metal bondings with heat resistance and high fracture strength, five items were experimentally investigated and could be summarized as follows: From screening tests of solder and interlayer materials for depression of thermal residual stress, triplex layer structures of Ti(1.5um)- Cu(20um)-Ni(a part of nickel interlayer) and of Ni(t)-W(t=1mm)-Ni(t=1mm) were finally selected as candidate solder and interlayer materials. It was found that a maximum fracture strength of 240MPa was obtained at room temperature when a thickness of nickel interlayer is about 1.3mm. This fracture strength increased with increase in test temperatures and reached about 290MPa at 400ﾟC and then decreased gradually, but it is still higher than 180MPa at 800ﾟC. The bonding was heated at 1000ﾟC up to 100hr in vacuum and showed little change in fracture strength and raction bonding layer structures. In oxidizing atmospheres as in air it was found that a high fracture strength of this bonding was k … More ept up to 600ﾟC and above this critical temperature a fracture strength decreased rapidly due to the selective oxidation of the tungsten layer. Instead of tungsten an interlayer with anti-oxidation property has to be developed and is now under progress.A ultra-sound microscope was used for non-destructive evaluation of thermal residual stress developed on the ceramic surface when it was joined to metals. The principle of this method is to measure velocity of leaky surface acoustic wave, which changes dependent on stress conditions, namely, the velocity decreases with tension stress and the reverse case is for compressive stress. This novel technique enables us to measure stress distribution in the vicinity of ceramic/metal bonding interface. The results obtained are reasonable, except several new findings which is unexplainable using existing knowledges. In order to understand these new results further theoretical and experimental investigations should be required and are under progress in our laboratory. Less