• PDF / 5,728,827 Bytes
• 6 Pages / 612 x 792 pts (letter) Page_size
• 104 Downloads / 280 Views

DOWNLOAD

REPORT

---

BB5.11.1

Effect of Antiphase Domain Boundaries on Prism Slip in Ti3Al Single Crystals Y. Koizumi 1*, Y. Minamino1, N. Tsuji1, T. Nakano2 and Y. Umakoshi2 1 Department of Adaptive Machine Systems, Osaka University 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan 2 Department of Materials Science and Engineering, Osaka University 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan ABSTRACT Effect of antiphase domain boundaries (APDBs) on yielding and dislocation structure were investigated in Ti3Al single crystals oriented for prism slip. The yield stress greatly depended on the size of antiphase domains (APDs). The yield stress of Ti3Al with the average APD size of 35nm was about six times higher than that of Ti3Al without APDB. Single dislocations (isolated superpartial dislocations) were observed in the deformed Ti3Al single crystal with APD sizes smaller than 100nm, while superdislocation pairs were observed in those with larger APDs. The mechanism of the interaction between the prism dislocations and APDBs is discussed. INTRODUCTION It has been known that mechanical properties of some intermetallic compounds are affected by antiphase domain boundary (APDB). For example, the yield stress of Cu3Au can be raised up to twice of that of Cu3Au without APDB [1]. Bend ductility of rapidly-solidified Fe-doped Ni3Al, which contains fine APDs, is about ten times larger than that of B-doped Ni3Al with coarse APDs [2]. Ti3Al is a kind of intermetallic compounds in which APDB can be formed during the ordering process [3-5]. There is no study on the effect of APDB on the mechanical property of Ti3Al, although there are many studies on the plastic deformation behavior of fully ordered Ti3Al, that is, Ti3Al without APDB [6-10]. Operative slip systems and their characteristics have been The {1 1 00} < 1120 > prism slip, clarified in the previous studies of the fully ordered Ti3Al. the (0001) < 1120 > basal slip and the {112 1} < 112 6 > pyramidal slip are operative depending on the loading axis. The prism slip can operate very easily, while others can operate under limited stress conditions. In this study, the effect of APDB on yield stresses of Ti3Al single crystals oriented for the prism slip was investigated. Microstructure observation was also carried out by TEM in order to clarify the interaction between APDB and dislocation motion.

*

Corresponding author. tel&fax: +81-6-6879-7434. E-mail address:[email protected] (Y. Koizumi)

BB5.11.2

EXPERIMENTAL PROCEDURES The procedure for obtaining Ti3Al single crystal with stoichiometric composition (Ti-25.0at%Al) was identical to that reported previously [11]. Single crystals sliced to 2.5mm thick were enclosed in quarts capsules under a vacuum. They were held at 1423K for 1.8ks in order to obtain disordered state and subsequently water-quenched with the capsules broken. For APD size control, the crystals were annealed at 1173K for various times. The annealing times and the resultant APD sizes are listed in Table 1. Note that there are quite small APDs even in the as-quenched s