Study of the microstructure and oxidation of NbSi{sub 2} base alloys
- Univ. of Surrey, Guildford (United Kingdom). Dept. of Material Science and Engineering
The microstructures of arc melted ingots and melt spun ribbons of NbSi{sub 2} and NbSi{sub 2}-(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 Nb{sub 5}Si{sub 3} in Zone A of the binary alloy ribbons. In the ternary alloy ingots and ribbons formation of the Nb{sub 5}Si{sub 3} was suppressed, and the C40 NbSi{sub 2} and CrSi{sub 2} and orthorhombic Nb{sub 2}Si{sub 6}Cr{sub 3} phases were formed. Zone A was not formed in the ribbons of the ternary alloys. The microhardness of these phases and the oxidation behavior of the alloys up to 1350 C in air and an Ar atmosphere are discussed. NbSi{sub 2} did not form a protective silica layer on oxidation. Instead a mixed oxide scale of silica and {alpha}-Nb{sub 2}O{sub 5} 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 SiO{sub 2} and Cr{sub 2}O{sub 3} and that the underlying matrix becomes depleted in Cr. Pest oxidation at 750 C was suppressed in Nb-60Si-20Cr.
- OSTI ID:
- 72553
- Report Number(s):
- CONF-941144--; ISBN 1-55899-265-0
- Country of Publication:
- United States
- Language:
- English
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