Phase-Field Simulation of Antiphase Boundary Migration in Intermetallic Compounds with Solute and Vacancy Segregation
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Phase-Field Simulation of Antiphase Boundary Migration in Intermetallic Compounds with Solute and Vacancy Segregation Yuichiro Koizumi1, Tatsuya Yokoi2, Masayuki Ouchi2, Yoritoshi Minamino2, Masato Yoshiya2 and Samuel M. Allen3 1 Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-0011, Japan 2 Department of Adaptive Machine Systems, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan 3 Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA ABSTRACT The effects of solute and vacancy segregation on APB migration in Ti3Al, and their dependence on composition, have been investigated by using a phase-field simulation in which vacancy distribution is taken into account. Al-atoms are depleted and vacancies segregate at APB in stoichiometric Ti3Al (Ti-25Al), whereas Al-atoms segregate and vacancies are depleted in Alrich one (Ti-28Al). The simulation indicates that APB in Ti3Al migrates much faster in Ti-25Al than in Ti-28Al with the effect of vacancy segregation whereas it migrates slightly faster in Ti28Al than in Ti-25Al in the absence of the effect of vacancy segregation. INTRODUCTION The mechanical properties of some intermetallic compounds are significantly affected by thermal antiphase boundaries (APBs). The critical resolved shear stress for {11̅00} slip of Ti3Al containing a high density of thermal APBs can be increased up to 6 times larger than that of an APB-free (i.e. single domain) counterpart [1]. Giant pseudoelasticity is manifested by the interaction between dislocations and fine-scale antiphase domains (APDs) in Fe3Al and Fe3Ga [2-4]. However, to apply these attractive mechanical properties to practical use at elevated temperatures, the stability of the fine thermal APD structure becomes important since the coarsening of APDs degrades such attractive properties. A key factor for the stability of thermal APDs is segregation to APBs. For instance, we detected segregation of solute atoms at APBs in Ti3Al [5]. Such segregation may cause solute-drag and affect the apparent mobility of APBs. Furthermore, voids were observed along thermal APBs in CuZn [6], implying that vacancies segregate at APBs, and such vacancy segregation may accelerate APB migration by enhancing the atomic rearrangement near the APBs. Controlling these segregations may allow us to improve the thermal stability of APDs. However, it is difficult to examine the effect segregation on APB migration experimentally because the measurement of local solute concentration in nanometer scale is of great difficulty, and measuring local vacancy concentration is impossible at this moment. In the latest studies [7,8], we have developed a phase-field simulation in which the local vacancy concentration is taken into account, and it was applied to the migration of APBs in Fe3Al. It has been revealed that the migration of B2-APB and D03-APB were affected by solute and vacancy segregation in different manners [8]. In addition
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