Orientation Dependence of the Texture Evolution in Cold-Rolled Thin Foils of Ni 3 Al Single Crystals
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Orientation Dependence of the Texture Evolution in Cold-Rolled Thin Foils of Ni3Al Single Crystals Kyosuke Kishida, Masahiko Demura. Yozo Suga*, and Toshiyuki Hirano Materials Engineering Laboratory, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, JAPAN * Nippon Cross Rolling Corporation, 697 Mobara, Mobara, Chiba 297-0026, JAPAN ABSTRACT Texture evolutions of cold-rolled thin foils of binary stoichiometric Ni3Al single crystals were examined as a function of the initial crystal orientation. In the cases of the initial rolling direction (RD) close to , the rolling texture above 90% reduction is composed of two {110} textures, which resulted from the formation of the banded structure with two types of differently oriented matrix bands. The macroscopic shape of these cold-rolled foils is straight and simply elongated along RD keeping their rectangular shape. In contrast, when the initial RD is close to , the texture and the microstructure are rather uniform but the foils are curved, twisted, and eventually cracked from the side edge of the samples. Based on the analysis of the texture evolution and the microstructure observation, the operative slip systems were determined. INTRODUCTION We have successfully fabricated thin foils of binary stoichiometric Ni3Al below 100µm in thickness simply by cold rolling unidirectionally solidified (UDS) ingots [1]. Maximum cold reductions above 96% have been achieved without intermediate annealing. The as-rolled foils have quite smooth and shiny surfaces. It should be noted that these as-rolled foils exhibit some bend ductility, which is sufficient to form corrugation required for the honeycomb structure fabrication. Furthermore, the foils possess some room-temperature tensile ductility (3.0 ~ 14.6%) in air after recrystallization [1]. Thus, these previous results demonstrate a high potential of our Ni3Al foils for applications in a form of the honeycomb structure, for example, as automotive exhaust gas catalysts supports. Since our UDS ingots are single crystals in most cases, it is important to elucidate the relationship between the initial crystal orientations and the cold rolling behavior. For this purpose, the textures and the microstructures in thin foils of binary Ni3Al fabricated from ingots with various initial orientations were examined by the X-ray Shultz reflection method, and optical (OM) and transmission electron microscopy (TEM), respectively. EXPERIMENTAL DETAILS UDS ingots were grown from binary Ni3Al with a nominal composition of Ni-25at%Al using optical floating zone furnace at a growth rate of 25mm/h. The growth directions (GDs) of the UDS ingots used in this study were close to either [001] or [¯ 112]. Specimens for cold rolling
Mat. Res. Soc. Symp. Proc. Vol. 753 © 2003 Materials Research Society
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with a thickness of 1 or 2mm were sectioned from the as-grown ingots by electric discharge machining so that their RD became parallel to the GD of the as-grown UDS ingot. The initial orientations of the specimen
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