Microstructural stability on aging of an α + β titanium alloy: ti- 6ai- 1.6zr-3.3mo- 0.30si |
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Authors: | A K Singh T Roy C Ramachandra |
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Affiliation: | (1) Defence Metallurgical Research Laboratory, 500 258 Hyderabad, India;(2) Foundry and Forge Division, Hindustan Aeronautics Limited, 560 017 Bangalore, India |
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Abstract: | The development of the microstructure on aging of an (α + β) type titanium alloy containing 6A1-1.6Zr-3.3Mo-0.3Si (VT9) (in
weight percent) has been studied. The β-transus temperature of this alloy is approximately 1243 K. Solution treatment in the
β-phase field of the alloy followed by quenching in water at room temperature resulted in the formation of a single-phase
martensite struc-ture. The martensitic structure was confirmed to be orthorhombic (α″) using X-ray diffraction. The water-quenched
(WQ) specimens were subjected to aging treatments at temperatures of 823, 873, and 973 K for various lengths of time. Aging
at 823 K for times between 24 and 100 hours did not bring about any noticeable change in the microstructure. Aging at 823
K for 200 and 300 hours resulted in the heterogeneous precipitation ofs
2 silicide particles and thin films of β sandwiched between the interplatelet boundaries of martensite. Electron diffraction
analysis confirms that the crystal structure of silicide particles is hexagonal with lattice parameters α= 0.70(1) nm andc = 0.36(8) nm. Aging at 873 K for 12 and 24 hours resulted only in the precipitation ofs
2 silicide particles, while aging at the same temperatures for longer times (48, 100, and 200 hours) and also at 973 K for
6 to 100 hours resulted in the precipitation of silicides and also thin films of β and acicular martensite. The relative sizes
of silicide precipitates and width of thin films of β phase increase with increasing aging time. The sites for silicide precipitation
are mainly at α′-α′ boundaries, α-β interfaces, and sometimes within regions of transformed β. The kinetics ofs
2 silicide precipi-tation in this alloy is faster than in commercial near-α titanium alloys. This is attributed to the presence
of Mo, a strong β stabilizer.
Formerly Reader, Department of Metallurgical Engineering, Centre of Advanced Study, Institute of Technology, Banaras Hindu
University, Varanasi-221 005, India |
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