Ti-6Al-2Sn-4Zr-2Mo-0.1Si specimens were shaped by repeated cycles of heating
(to 954 °C) and hammer or press forging followed by a solution anneal that varied from
968 to 998 °C. The coupons were originally extracted from billets forged below the beta
trans us ( 1009 °C) and slow cooled to ambient temperature. Macroscopic and
microstructural banding is observed in some forged and solution annealed coupons, that
consists of regions of elongated primary alpha. More significant banding is observed
subsequent to annealing at lower temperatures (968 °C), whereas much less microstructural
banding is present after annealing at higher temperatures (998 °C). About the same level of
banding is observed in hammer forged and press forged coupons. The observation of these
bands is significant since they may lead to inhomogeneous mechanical properties.
Specifically, at least some types of banding are reported to affect the high temperature creep
properties of this alloy. The origin of these bands was therefore researched. Classically,
banding in Ti-6242-0.1Si has been regarded as a result of adiabatic shear, chill zone
formation or compositional inhomogeneity. High and low magnification metallography,
electron microprobe analysis and microhardness tests were performed on forged and
annealed specimens in this investigation. The composition inside the bands appears
identical to that outside of the bands. The fraction of primary alpha is also found to be
identical. The bands have higher microhardness. These results suggest that the bands are
not related to composition gradients. The bands also do not appear to be a result of
adiabatic shear or other localized deformation. The bands of this study appear to originate
from the elongated primary alpha microstructure of the forged billet (from which test
coupons were extracted). The deformation of the extracted coupon may be neither fully
homogeneous nor sufficiently substantial and the coupon is only partly statically restored
after a solution anneal. Areas not fully restored appear as "bands" with elongated primary
alpha, that are remnant of the starting billet microstructure. Therefore, a source of banding
in Ti-6242-0.1Si alloy, additional to the classic sources, is evident. This type of banding is
likely removed by relatively high solution treatment temperatures and perhaps greater
plastic deformation during forging. / Graduation date: 1992
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/36678 |
| Date | 21 January 1992 |
| Creators | Kansal, Utkarsh |
| Contributors | Kassner, M. E. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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