Ex Situ Observation of Microstructure Evolution During Abnormal Grain Growth in Aluminum Alloy
- PDF / 684,248 Bytes
- 6 Pages / 593.972 x 792 pts Page_size
- 48 Downloads / 274 Views
I.
INTRODUCTION
ABNORMAL grain growth (AGG), which is also referred to as secondary recrystallization, frequently occurs in metallic materials. During AGG, only a few grains grow abnormally, consuming the neighboring matrix grains, which results in an intermediate duplex microstructure consisting of large abnormally grown grains and small matrix grains. Since properties of polycrystalline materials depend strongly on their microstructure such as the grain size and the texture, extensive efforts have been made to understand the mechanism of AGG. This phenomenon is particularly famous in Fe-3 pct Si steel because the core loss of Fe-3 pct Si in the application such as an electrical transformer can be reduced by properly controlling AGG.[1–3] Since the first report of the selective AGG of Gossoriented grains in Fe-3 pct Si steel by Goss in 1935,[4] the mechanism has not yet been clearly understood. Most of those efforts were focused on the coincidence site lattice (CSL) boundaries shared by Goss grains. Based on the CSL theories, the AGG takes place via local consumption of grains with CSL relationships by Goss grains during secondary recrystallization, although there is some controversy as to a role of CSL boundaries. Harase and Shimizu[5]Psuggested that Goss grains have high frequency of 9 relationship with matrix P grains. The 9 boundaries are considered to have HYUNG-KI PARK, formerly Ph.D. Student with the Department of Materials Science and Engineering, Seoul National University, Seoul 151-742, Korea, is now Researcher with POSCO Technical Research Laboratories, POSCO, Pohang 790-360, Korea. HYUNG-GU KANG, Researcher, is with POSCO Technical Research Laboratories. CHANG-SOO PARK, Ph.D. Student, and NONG-MOON HWANG, Professor, are with the Department of Materials Science and Engineering, Seoul National University. Contact e-mail: nmhwang@ snu.ac.kr MOO-YOUNG HUH, Professor, is with the Department of Materials Science and Engineering, Korea University, Seoul 136-713, Korea. Manuscript submitted January 9, 2012. Article published online August 3, 2012 5218—VOLUME 43A, DECEMBER 2012
higher mobility than general grain boundaries. Therefore, AGG occurs consuming neighboring grains, which P have 9 relationship with the secondary Goss grains. However, instead of focusing on the high mobility of P 9 boundaries, Homma and Hutchinson[6] focused on the low energy of them. They suggested P that Goss grains with high frequency of low-energy 9 boundaries with matrix grains have an advantage to unpin Zener drag by second-phase particles. Similarly, Maazi and Penelle[7] reported that Goss grains have high frequency of CSL boundaries, which have relatively low energy, and therefore, it has an advantage to overcome Zener drag during secondary recrystallization. On the other hand, a totally different explanation for AGG, which is called solid-state wetting, has been suggested, where the growth advantage of abnormally growing grains is approached in terms of the grain boundary energy.[8–12] The grain boundary migration is driven by the
Data Loading...
