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Amorphization at the Metal-Ceramic Interface in Nb – Al2O3 Composite Through Extensive Interphase Diffusion

Published online by Cambridge University Press:  25 February 2011

Abhijit Ray
Affiliation:
Mechanical Engineering Department, Plasticity Laboratory, University of Nevada-Reno, NV-89557.
Shyam K. Samanta
Affiliation:
Mechanical Engineering Department, Plasticity Laboratory, University of Nevada-Reno, NV-89557.
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Abstract

A novel, low temperature and pressureless bonding technique has been developed to fabricate Al2O3 coated Nb composite. The nature of the interface bond has been characterized by extensive electron microscopic investigation, and a phenomenological model has been developed to explain the mechanism of bond formation. In the present technique a suspension (in distilled water) of fine Al2O3 powder (mean particle size of 0.2μm) was applied on polished and cleaned Nb blocks. The coatings were air dried and the coated metals were heat treated at 1100°C to achieve bonding between the ceramic and the metal. The process was carried out in an argon atmosphere. To reduce the oxygen impurity content in argon, the gas was passed over Mg turnings at 300°C before its entry into the bonding apparatus. Control of oxygen impurity in the bonding atmosphere in conjunction with the use of fine ceramic particles led to enhancement of interfacial diffusion. Scanning electron microscopy of the bonded specimens showed a consolidated layer in the ceramic phase close to the metal-ceramic interface. Transmission electron microscopy of the metal-ceramic interfacial region rOevealed a distribution of Al2O3 particles in an amorphous phase containing varying amount of Al, Nb, and 0. Prior treatment with Mg was to reduce the oxygen impurity content below the equlibrium oxygen partial pressure (at 1100°C) of Al2O3. This would result in loss of oxygen from the surface of the ceramic particles. Thus a region, with high concentration of 0= vacancy would form along the surfaces of the particles. As a result of excessive oxygen depletion, further continuation of this process would lead to degeneration of the crystal structure of the regions along the surfaces of the Al2O3 particles. These regions along the Al2O3 particle surfaces may then act as easy diffusion paths for Nb. Extensive diffusion of the metal into the ceramic phase along these paths would lead to the formation of an amorphous phase along the ceramic particle surfaces. Eventually, this phase will occupy the voids in between the ceramic particles, that are close to the metal-ceramic interface, and thus bond them together with the metal.

Type
Research Article
Copyright
Copyright © Materials Research Society 1992

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References

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