Effect of Al Concentration on Growth of Antiphase Domains in Ti 3 Al
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Effect of Al Concentration on Growth of Antiphase Domains in Ti3Al Y. Koizumi, H. Katsumura, Y. Minamino and N. Tsuji Department of Adaptive Machine Systems, Osaka University 2-1 Yamada-oka, Suita Osaka 565-0871, Japan ABSTRACT Effects of Al-concentration on growth of antiphase domains (APDs) in Ti3Al crystals have been investigated using crystals with stoichiometric (Ti-25at.%Al) and Al-rich (Ti-33at.%Al) compositions in the temperature range from 973K to 1173K. The growth rate of APDs in the Al-rich crystal is several times higher than that in the stoichiometric crystals at all the temperatures investigated. While the time dependence of APD size obeys the parabolic-growth-law in the stoichiometric crystal, negative deviations from the law takes place at the late stage of the APD growth in the Al-rich crystal owing to the pinning effect of low-energy APB boundaries. APD boundaries lying on prism planes are formed in the Al-rich crystal annealed at 973K. INTRODUCTION Antiphase domains (APDs) can be formed in the ordering process of many intermetallic compounds with ordered structure. Their boundary (APD boundary or simply antiphase boundary: APB) is a planar defect originating from fault in ordered arrangements of different atom species. They often have remarkable influences on properties of materials, such as electrical property [1], magnetic property [2] and mechanical property [3]. The influence of APDs on mechanical property is quite remarkable in Ti3Al with D019-type ordered structure [4]. The yield stress of Ti3Al single crystals by prism slip conspicuously varies from 130MPa to 740MPa depending on the average size of antiphase domains (APDs), that is the domains surrounded by APBs. Furthermore, quite unique dislocation arrangements, in which dislocations were greatly winding along the APD boundaries, were observed. This means that dislocation arrangement in Ti3Al can be artificially controlled by means of controlling the morphology of the APBs since APBs can tightly trap prism dislocations in Ti3Al. The artificially arranged dislocations can give many kinds of unique and useful properties to this material. For example, they will realize completely reversible plasticity and ultra-high damping capacity which are based on synchronized flip-flop motions of superdislocation dipoles. In order to control the morphology of APBs aiming to make templates for the dislocation arrangement, it is required to know the factors which affect the morphology of APDs. However, little is known about the morphology of APDs in Ti3Al [5,6]. The objectives of this study are to investigate the growth behavior of APDs in stoichiometric and Al-rich Ti3Al crystals and to obtain information required for controlling the morphology of APDs. Y7.10.1
EXPERIMENTAL PROCEDURES Ti3Al single crystals with stoichiometric composition (Ti-25at.%Al) and Al-rich composition (Ti-33at.%Al) were prepared by the procedure reported previously [7]. The single crystals were sliced to 2.5mm thick, and sealed in quartz capsules pure argon of 2×104 Pa. They wer
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