Papers by Author: Yoshihiro Terada

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Authors: Naoki Ohashi, Takashi Sekiguchi, Hajime Haneda, Yoshihiro Terada, Takeshi Ohgaki, Takaaki Tsurumi, M. Tanaka, O. Fukunaga
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Authors: Takashi Sekiguchi, Naoki Ohashi, Yoshihiro Terada
1371
Authors: Masaomi Mitsutake, Yoshihiro Terada, Takashi Matsuo
Abstract: The features of the creep deformation of γ-single phase single crystals with the composition of Ni-20mass%Cr are characterized by the extended transient stage, which consists of Stage I and Stage II. In the Stage I, the creep rate just after loading remains unchanged, while the creep rate decreases continuously in Stage II. In the single crystals except for the single crystals with the stress axis of [001] and [1, – 11], the predominant creep deformation using the primary slip plane continues. By this deformation, the cross section of specimen turns to elliptical in shape. However, in the single crystals with the angle between stress axis and primary slip plane (111) is more than 45°, the deformation using the primary slip plane does not continue, as a result, the duration of Stage II turn to shorter one. The single crystal with the stress axis of [011] has the largest angle of 55°. In this study, the deformation manner during transient stage of single crystal with the stress axis of [011] orientation is investigated from the two viewpoints. The first one is to clarify the change in deformation manner with decreasing the stress. As a result, with decreasing the stress, the Stage I become clear and strain during Stage I and Stage II become small, furthermore, the decreasing ratio of creep rate with definite strain becomes larger. While, the second viewpoint is to investigate the change in crystallographic orientation of the [011] single crystals with creep deformation using the inverse pole figure obtained by the EBSD method. As a result, at the stress of 29.4 MPa, the spot of stress axis turns from the [011]-[1, – 11] line to the <1, – 01> direction. While, at the stress of 19.6 MPa, the stress axis moves for the [1, – 11] pole along the [011]-[1, – 11] line from the [011] pole. And, it is noteworthy that the spot widely spread from the [011] pole during transient stage. This indicates the large distortion in the primary slip plane and the evidence of heterogeneous deformation.
870
Authors: Kentaro Yuge, Yoshihiro Terada, Takashi Matsuo
Abstract: The creep deformations of γ-single phase Ni-20mass%Cr single crystals with stress axes within standard stereographic triangle and at the three pole positions have been investigated. The most of the creep life is occupied by the transient stage, which consists of Stage I and Stage II. In Stage I, the creep rate just after loading remains constant. In Stage II, the creep rate decreases continuously. Except for the single crystals with stress axes of [001] and [1,–11] poles, the single crystals make the creep deformation using the primary slip plane of (111). As a result, the cross section of the specimens turns from circular to elliptical in shape. However, there are marked difference in deformation manner among single crystals with the stress axes within standard stereographic triangle. The single crystals whose angle between stress axis and primary slip plane of (111), θ. is more than 45° shows the heterogeneous deformation during creep. While, the homogeneous deformation will be expected in the single crystals with θ less than 45°. In this study, by using the four single crystals with θ less than 45°, the change in the stress axis with the creep deformation at 1173K-29.4MPa, is investigated and the deformation manner due to the primary slip plane of (111) is estimated by conducting the creep interrupting tests. In the two single crystals with stress axes in the standard stereographic triangle where the moving range of θ is narrow, comparing to the others, the spot of the stress axis in the inverse pole figure moves for <1,– 01> direction by using (111)<1,–01> slip system, and after arriving at the [001]-[1,–11] line, the spot turns to its direction for [1,–11] pole using (111)<1,–10> slip system. While, in the other two single crystals whose stress axes located in the area with wider moving range of θ, the spot of stress axis only move for <1,–01> direction. And, the widely spread spot of the stress axis is confirmed after subjecting the small strain.
864
Authors: Yoshihiro Terada, Naoya Ishimatsu, Rie Sota, Tatsuo Sato, Koichi Ohori
459
Authors: T. Matsuo, S. Takahashi, Y. Ishiwari, Yoshihiro Terada
553
Authors: Yoshihiro Terada, Takeshi Yasui, Takashi Matsuo
785
Authors: Yoshihiro Terada, Tatsuo Sato
Abstract: Creep rupture tests were performed for a die-cast Mg-Al-Ca alloy AX52 (X representing calcium) at 29 kinds of creep conditions in the temperature range between 423 and 498 K. The creep curve for the alloy is characterized by a minimum in the creep rate followed by an accelerating stage. The minimum creep rate (ε& m) and the creep rupture life (trup) follow the phenomenological Monkman-Grant relationship; trup = C0 /ε& m m. It is found for the AX52 die-cast alloy that the exponent m is unity and the constant C0 is 2.0 x 10-2, independent of creep testing temperature. The values of m and C0 are compared with those for another die-cast magnesium alloys. The value m=1 is generally detected for die-cast magnesium alloys. On the contrary, the value of C0 sensitively depends on alloy composition, which is reduced with increasing the concentration of alloying elements such as Al, Zn and Ca.
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