Texture Memory Effect During Heat Treatment in the Heavily Cold Rolled Ni 3 Al Foils
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0980-II01-09
Texture Memory Effect During Heat Treatment in the Heavily Cold Rolled Ni3Al Foils Masahiko Demura1, Ya Xu1, Kyosuke Kishida2, and Toshiyuki Hirano1 1 Fuel Cell Materials Center, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki, 305-0047, Japan 2 Department of Materials Science and Engineering, Kyoto University, Sakyo-ku, Kyoto, 6068501, Japan
ABSTRACT Texture evolution during grain growth was examined in the 84% cold-rolled Ni3Al with a Goss texture, {110}, using the electron backscatter diffraction method. By recrystallization at 873K/0.5h, the texture was disintegrated and composed of several orientations, most of which had a 40˚ rotation relationship about to the Goss orientation. Also, a small number of the Goss grains existed. With grain growth, the Goss grains grew faster than the 40˚ rotated grains, leading to the texture reversion to the original, Goss texture. This phenomenon can be referred to Texture memory effect. In the early stage of the grain growth, the preferential growth occurred on the Goss grains surrounded by the 40˚ rotated grains. It can be thus ascribed to the high mobility of 40˚ grain boundary. In the late stage, the Goss grains were adjacent to each other and the preferential growth was accelerated. It is considered that the adjacent Goss grains survived in the grain coalescence process since the boundary between them are low angle boundary having a low energy. INTRODUCTION Thin foils of boron-free Ni3Al intermetallics have been developed for high-temperature micro systems [1]. We have recently found an interesting texture evolution during heat treatment in the cold-rolled Ni3Al foils (Figure 1) [2]: disintegration by the primary recrystallization (Figure 1 (b)) and reversion to the original cold-rolled texture during the grain growth (Figure 1(c)). This two-step texture evolution can be referred to texture memory effect, which is crucial to improve the ductility of the foils [3]. Very recently, we have found that the texture disintegrated by the primary recrystallization has a 40˚ rotation relationship about to the original, cold-rolled texture [4]. This finding indicates that the 40˚ rotated grains can grow faster than the other in the deformation matrix; the preferential growth of the 40˚ rotated grains in the primary recrystallization is frequently observed in fcc metals [5]. Then, probably due to the same mechanism, the grains with the original, cold-rolled texture grow preferentially in the 40˚ rotated texture. In this paper, we examine the texture evolution during grain growth by the electron backscatter diffraction (EBSD) method and clarify the mechanism of the texture reversion. We here use the 84% cold-rolled foils with the Goss texture, which exhibits a homogeneous deformation microstructure without texture splitting. Thus, we can easily trace the grains with the original, Goss texture and the 40˚ rotated grains to determine the growth behavior of them.
Figure 1. X-ray {220} pole figures for the 84% cold-rolled Ni3Al single crystals: (a)
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