The nickel-alumina system has been considered extensively as a candidate metal-ceramic composite for high temperature structural applications since both materials exhibit favorable high temperature properties. As in other composite materials the strength of the interface is one of the key factors in determining the performance of the composite. Thus far, the performance on nickel-alumina composites has been mixed, the toughness of the composite can be as much as three times the toughness of pure alumina, but only for relatively large volume fractions of metal, see ref.[1] for example.

Part of the reason for the limited increase in toughness with the addition of metal appears to be a relatively weak bond between the nickel and alumina[2]. We are performing interfacial fracture toughness tests using thick (1-2mm) nickel foils sandwiched between alumina blocks, and bonded at high temperature under a controlled, reducing atmosphere. The thick metal foil allows us to propagate cracks along the metal-ceramic interface. With thinner foils we always observed the cracks deviating into the ceramic. Our experiments show that the interfacial toughness can be enhanced, by approximately a factor of two by small changes in the oxygen activity of the bonding atmosphere. Further experiments, over a larger range of atmospheres are underway. Three dimensional analyses of the test specimen including residual stresses, and stresses during the loading are being performed to gain further insight into the experiments.

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