Internal Friction of Austenitic Fe-Mn-C-Al Alloys
- PDF / 1,367,582 Bytes
- 9 Pages / 593.972 x 792 pts Page_size
- 22 Downloads / 196 Views
TRODUCTION
THE internal friction (IF) of face-centered-cubic (fcc) materials, which is related to anelastic relaxation (AR) caused by the reorientation of the pairs of crystal defects under cyclic stress, was actively studied from the early 1950s[1–3] to approximately 1970.[4] However, for the past 50 years or more, studies of the IF of fcc materials were rare as far as the present authors searched, although we do not know the reason. Recently, the IF of fcc Fe-Mn-C alloys, which was already studied during the early 1950s, was investigated again because Fe-Mn-C-based twinning-induced plasticity (TWIP) steel, one of the next-generation advanced high strength steels, exhibits room-temperature dynamic strain aging, which is believed to occur by the interaction between dislocations and defect pairs.[5,6] Until now, four different defect pairs were reported to be responsible for AR in fcc materials: (1)
a substitiutional atom—an interstitial atom (s-i) pair,[3–7]
YOUNG-KOOK LEE and SANG-MIN LEE are with the Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Republic of Korea. Contact email: [email protected] SOHEE JEONG is with the Steel Plate Development 1 Team, R&D Center, Hyundai Steel Company, Dangjin-Si, Chungnam 31719, Republic of Korea. JEE-HYUN KANG is with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang, Gyeongbuk 37673, Republic of Korea. Manuscript submitted November 11, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS A
(2) (3) (4)
an interstitial atom—an interstitial atom (i-i) pair,[8–10] an interstitial atom—a vacancy (i-v) pair,[11] and a vacancy—a vacancy (v-v) pair.[12]
Whereas interstitial atom diffuses between neighbering interstitial sites for s-i and i-i pairs, vacancy flips between substitutional sites for i-v and v-v pairs. The activation energy (~0.87 eV) for vacancy diffusion in fcc austenitic Fe-Ni-C alloys is lower than that for interstitial atom diffusion (~1.43 eV for a C atom).[11] In addition, although the same interstitial atom or vacancy diffuses, the activation energy values for the reorientation of defect pairs are different from one another because the defect pairs have different chemical binding energies between their constituents. As a result, a critical temperature where a relaxation peak occurs, namely, a peak temperature of IF (Tp), should be different, depending on the type of operating defect pairs even in the same fcc matrix. For example, in the case of fcc Fe-Mn-C alloys quenched from high solution treatment temperatures, all five defect pairs mentioned previously can be introduced into a specimen because of quenched-in excess vacancies. Nevertheless, only a single IF peak was reported until now. The Tp of the IF peak is in between 473 K (200 C) and 573 K (300 C) for a frequency (f) of ~1 Hz[11] and increases to ~653 K (380 C) for f = 530 Hz and to ~690 K (417 C) for f = 1630 Hz.[6] This result shows a strong dependency of the Tp of the single IF peak on f. However, it is still unclear why only a s
Data Loading...
