TY - JOUR
T1 - Extremely Rapid Age Hardening in Ti-5Al-2Fe-3Mo Solution Treated at High α + β Temperature Region
AU - Kunieda, Tomonori
AU - Kohigashi, Yusuke
AU - Fujii, Hideki
AU - Takahashi, Kazuhiro
AU - Takemoto, Yoshito
N1 - Publisher Copyright:
© 2021, The Minerals, Metals & Materials Society and ASM International.
PY - 2021/10
Y1 - 2021/10
N2 - To investigate the age hardening behaviors in an α + β titanium alloy, Ti-5Al-2Fe-3Mo, microstructures after solution treatment at a temperature in the high α + β region, and subsequent aging at temperatures below or around 500 °C were analyzed by transmission electron microscopy (TEM) and atom probe tomography (APT). Age hardening depended on both aging temperature and time, and at a very early stage of aging, fluctuations of Ti and alloying elements occurred in the β phase with an interval of several nanometers. It is considered that spinodal decomposition occurred. Subsequently, an extremely fine acicular hexagonal-close-packed (hcp) phase having width similar to that interval was formed, which contributed to age hardening together with the internal stress fields created by spinodal decomposition. A model was proposed to explain the extremely rapid hardening phenomenon: O suppresses martensite transformation during cooling from the solution treatment temperature, and the extremely fine hcp phase is formed in a short time by shear transformation in the O-lean area created by spinodal decomposition. In the O-lean area, the martensite start (Ms) temperature increases as the O concentration decreases. The effect of β-phase stability on the microstructural evolution in the spinodal modulated structure was also discussed: Shear transformation and β zone formation may occur depending on the β-phase stability and O concentration distribution.
AB - To investigate the age hardening behaviors in an α + β titanium alloy, Ti-5Al-2Fe-3Mo, microstructures after solution treatment at a temperature in the high α + β region, and subsequent aging at temperatures below or around 500 °C were analyzed by transmission electron microscopy (TEM) and atom probe tomography (APT). Age hardening depended on both aging temperature and time, and at a very early stage of aging, fluctuations of Ti and alloying elements occurred in the β phase with an interval of several nanometers. It is considered that spinodal decomposition occurred. Subsequently, an extremely fine acicular hexagonal-close-packed (hcp) phase having width similar to that interval was formed, which contributed to age hardening together with the internal stress fields created by spinodal decomposition. A model was proposed to explain the extremely rapid hardening phenomenon: O suppresses martensite transformation during cooling from the solution treatment temperature, and the extremely fine hcp phase is formed in a short time by shear transformation in the O-lean area created by spinodal decomposition. In the O-lean area, the martensite start (Ms) temperature increases as the O concentration decreases. The effect of β-phase stability on the microstructural evolution in the spinodal modulated structure was also discussed: Shear transformation and β zone formation may occur depending on the β-phase stability and O concentration distribution.
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U2 - 10.1007/s11661-021-06395-2
DO - 10.1007/s11661-021-06395-2
M3 - Article
AN - SCOPUS:85111833158
SN - 1073-5623
VL - 52
SP - 4424
EP - 4437
JO - Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
JF - Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
IS - 10
ER -