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Study of The Microstructure and Oxidation of NbSi2 Base Alloys

Published online by Cambridge University Press:  22 February 2011

S.H. Pitman
Affiliation:
Department of Material Science and Engineering, University of Surrey, Guildford, GU2 5XH, United Kingdom
P. Tsakiropoulos
Affiliation:
Department of Material Science and Engineering, University of Surrey, Guildford, GU2 5XH, United Kingdom
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Abstract

The microstructures of arc melted ingots and melt spun ribbons of NbSi2 and NbSi2-(8,20 at%)Cr alloys are discussed. Rapid quenching from the melt refined the grain size of the alloys by two orders of magnitude and suppressed the formation of Nb5Si3 in Zone A of the binary alloy ribbons. In the ternary alloy ingots and ribbons formation of the Nb5Si3 was suppressed, and the C40 NbSi2 and CrSi2 and orthorhombic Nb2Si6Cr3 phases were formed. Zone A was not formed in the ribbons of the ternary alloys. The microhardness of these phases and the oxidation behaviour of the alloys up to 1350°C in air and an Ar atmosphere are discussed. NbSi2 did not form a protective silica layer on oxidation. Instead a mixed oxide scale of silica and α-Nb2O5 formed which cracked during growth of the oxide and hindered protection of the alloy. It is shown that the addition of Cr modifies the oxide to a duplex oxide of SiO2 and Cr2O3 and that the underlying matrix becomes depleted in Cr. Pest oxidation at 750°C was suppressed in Nb-60Si-20Cr.

Type
Research Article
Copyright
Copyright © Materials Research Society 1995

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