Silicide Precipitation in Alloy Ti-6AI-5Zr-0.5Mo-0.25Si |
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Authors: | C Ramachandra Vakil Singh |
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Affiliation: | (1) Department of Metallurgical Engineering, Institute of Technology, Banaras Hindu University, 221005 (U.P.) Varanasi, India |
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Abstract: | Silicide precipitation in the titanium alloy containing by wt pct 6Al-5Zr-0.5Mo-0.25Si (Alloy 685) has been investigated using
electron diffraction. The solutionizing temperature for this alloy is 1323 K. It is observed that no resolvable silicide precipitates
are present in the alloy as received, furnace cooled from 1323 K and aged at 823 K, or oil quenched from 1323 K and aged at
823 K. Specimen solutionized at 1323 K for 30 minutes followed by water quenching and aging at 923 K for 24 hours shows fine
precipitates at boundaries of α′ platelets. Diffraction analysis shows that the fine precipitates belong to two different
types of identifiable hexagonal silicides similar to those observed by Floweret al in the ternary Ti-5Zr-0.5Si alloy to be (TiZr)5Si3 and another of unknown stoichiometry. However, aging of the water quenched specimens for 24 hours at higher temperatures,
973 K and 1073 K, results in the precipitation of a silicide similar to the latter one. It is analyzed that this silicide
has lattice parameters a = 0.702 nm and c = 0.368 nm. Since aging at 973 K and 1073 K gives rise to precipitation of the same silicide, it is concluded that this is the stable
silicide in Alloy 685 in the temperature range investigated. |
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