INTERFACIAL REACTIONS IN LAYERED COMPOSITES OF Nb-Al2O3 AND Nb (1% Zr)-Al2O3 IN HIGH-TEMPERATURE ANNEALING

• Published in: Refractories and industrial ceramics Vol. 40; no. 5/6; pp. 203 - 207
• Main Authors: Sichinava, M A, Kobyakov, V P
• Format: Journal Article
• Language: English
• Published: 1999
• ISSN: 1083-4877
• DOI: 10.1007/BF02762284

Interactions between alumina and niobium and a niobium alloy (1% Zr) in layered composites during vacuum annealing over the temperature range 1770-2070 K were investigated. The samples were coaxial tubes with an outer diameter of 20 mm consisting of two thin-walled metal shells with an intermediate alumina layer of up to 500 micron thickness. The alumina layer was fabricated by plasma deposition, and the composite assembly was hot isostatically pressed at 1920 K under a pressure of 25 MPa, in an argon atmosphere. Annealing resulted in noticeable changes in the structure and the phase composition of the contact zone of the layers, the changes at the ends of the sample being different from those observed internally. In the closed positions intermetallic Nb3Al was observed, and Al2O3 was detected in the alloy, whilst in the open position mass was lost from the contact zone and a narrow clearance formed between the metal and the ceramic. It was concluded that the observed changes adversely affected the strength, continuity, and electrical resistivity of the composites. 26 refs.