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TiFe Precipitation Behavior and its Effect on Strengthening in Solution Heat-Treated Ti-5Al-3.5Fe During Isothermal Aging

1
Metal Materials Division, Korea Institute of Materials Science, Changwon 51508, Korea
2
School of Materials Science and Engineering, Busan National University, Pusan 46241, Korea
*
Author to whom correspondence should be addressed.
Metals 2018, 8(11), 875; https://doi.org/10.3390/met8110875
Received: 16 October 2018 / Revised: 23 October 2018 / Accepted: 24 October 2018 / Published: 26 October 2018
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)
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Abstract

We investigated the TiFe precipitation behavior of solution heat-treated Ti-5Al-3.5Fe during isothermal aging, quantified the effect of precipitation on strengthening by evaluating the hardness, and compared it to the effect of Ti3Al precipitation in Ti-6Al-4V. TiFe precipitates formed both at grain boundaries (GBs) and within the grain matrices. Phase transformation from the β to α phase also occurred during isothermal aging; this transformation generated lamellar interphase boundaries between the transformed α phase and remaining β phase in prior β grains. These interphase boundaries enabled the formation of in-grain TiFe precipitates by acting as a nucleation site. GB precipitation did not require prior βα phase transformation to generate nucleation sites (i.e., interphase boundaries), so TiFe precipitation could occur immediately upon isothermal aging. Thus, GB precipitation proceeded more quickly than in-grain precipitation; as a result, precipitates were larger and more spherical at the GBs than in grains. The strengthening behavior exhibited by TiFe precipitation differed obviously from that caused by Ti3Al precipitation in Ti-6Al-4V because of its differing precipitation kinetics and related microstructural evolution. View Full-Text
Keywords: titanium alloys; precipitates; phase transformation; hardness titanium alloys; precipitates; phase transformation; hardness
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Choe, H.-J.; Won, J.W.; Hyun, Y.-T.; Lim, K.R.; Yoon, S.-Y. TiFe Precipitation Behavior and its Effect on Strengthening in Solution Heat-Treated Ti-5Al-3.5Fe During Isothermal Aging. Metals 2018, 8, 875.

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