SOLID-STATE BONDING OF ACCURATELY ORIENTED METAL CERAMIC BICRYSTALS IN ULTRAHIGH-VACUUM

A machine is described which allows bicrystals of metals and ceramics to be made by pressure bonding at temperatures up to 1500-degrees-C in ultrahigh vacuum (UHV). The mutual orientation of the two component crystals can be adjusted to within 0.1-degrees. The surfaces to be bonded can be sputter cleaned with Ar ions while monitoring by Auger electron spectroscopy, and dopants can be applied by evaporation in a separate chamber. The machine allows the production of bicrystals with interfaces of precisely defined crystallography and chemistry. The specimen size is sufficient for fracture mechanical characterization of interface strength. The performance of the machine is illustrated with data for niobium-sapphire bicrystals. The machine has been shown to produce bicrystal interfaces whose purity is not measurably impaired by atmospheric contaminants. Fracture resistant levels of Nb-Al2O3 interfaces bonded at 1700-degrees-C in ordinary high vacuum are reached in the UHV machine already at 1000-degrees-C. Going to temperatures around 1450-degrees-C raises the fracture resistance to more than twice the level obtained in ordinary hi vacuum at 1700-degrees-C.