On the decomposition of {beta} phase in some rapidly quenched titanium-eutectoid alloys
- National Aerospace Lab., Bangalore (India). Materials Science Div.
- Indian Inst. of Science, Bangalore (India)
The decomposition of the {beta} phase in rapidly quenched Ti-2.8 at. pct Co, Ti-5.4 at. pct Ni, Ti-4.5 at. pct, and 5.5 at. pct Cu alloys has been investigated by electron microscopy. During rapid quenching, two competitive phase transformations, namely martensitic and eutectoid transformation, have occurred, and the region of eutectoid transformation is extended due to the high cooling rates involved. The {beta} phase decomposed into nonlamellar eutectoid product (bainite) having a globular morphology in Ti-2.8 pct Co and Ti-4.5 pct Cu (hypoeutectoid) alloys. In the near-eutectoid Ti-5.5 pct Cu alloy, the decomposition occurred by a lamellar (pearlite) type, whereas in Ti-5.4 pct Ni (hypereutectoid), both morphologies were observed. The interfaces between the proeutectoid {alpha} and the intermetallic compound in the nonlamellar type as well as between the proeutectoid {alpha} and the pearlite were often found to be partially coherent. These findings are in agreement with the Lee and Aaronson model proposed recently for the evolution of bainite and pearlite structures during the solid-state transformations of some titanium-eutectoid alloys. The evolution of the Ti{sub 2}Cu phase during rapid quenching involved the formation of a metastable phase closely related to an ``{omega}-type`` phase before the equilibrium phase formed. Further, the lamellar intermetallic compound Ti{sub 2}Cu was found to evolve by a sympathetic nucleation process. Evidence is established for the sympathetic nucleation of the proeutectoid {alpha} crystals formed during rapid quenching.
- OSTI ID:
- 78406
- Journal Information:
- Metallurgical Transactions, A, Journal Name: Metallurgical Transactions, A Journal Issue: 6 Vol. 26; ISSN 0360-2133; ISSN MTTABN
- Country of Publication:
- United States
- Language:
- English
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