Room Temperature Ductility of B2-Type CoZr Intermetallic Compounds
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0980-II06-11
Room Temperature Ductility of B2-Type CoZr Intermetallic Compounds Yasuyuki Kaneno1, Takayuki Takasugi1, Mitsuhiko Yoshida2, and Hiroshi Tsuda1 1 Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 5998531, Japan 2 Department of Materials Science and Engineering, Miyagi National College of Technology, Natori, Miyagi 9811239, Japan
ABSTRACT B2 (CsCl) CoZr intermetallic alloys with different chemical compositions were hot-rolled and subsequently recrystallized to evaluate tensile properties and rolling workability. Co-49.0Zr, -49.5Zr and -50.0Zr alloys showed the B2-matrixed microstructure containing C15 Co2Zr dispersions, while Co-50.5Zr and -51.0Zr alloys showed the B2-matrixed microstructure containing C16 CoZr2 dispersions. These homogenized ingots were successfully hot-rolled without edge cracks, except for the Co-51.0Zr alloy. The tensile tests revealed that the Co49.5Zr, -50.0Zr and -50.5Zr alloys exhibited a notable tensile ductility at room temperature as well as at elevated temperatures. Moreover, the recrystallized CoZr alloys were cold-rolled up to 70% reduction without intermediate annealing. It was also found that tensile ductility was most prominent in the Co-50.0Zr alloy with the least volume fraction of second phase dispersions in the investigated alloys, suggesting that the B2 phase of CoZr was inherently ductile. Deformation microstructures were characterized by means of XRD and TEM observations. Mechanisms responsible for the observed large tensile ductility of the CoZr alloys were discussed, on the basis of the observed deformation microstructures. INTRODUCTION B2 intermetallic alloys generally have low ductility at low temperature in spite of relatively simple crystal structure. However, it has been recently reported that just-stoichiometric B2 ordered intermetallic compounds (e.g. YAg), which are commonly composed of a rare earth metal and a late transition group or a group II, III, or IV metal, display remarkable room temperature tensile ductility more than 20% before fracture [1]. On the other hand, a polycrystalline CoZr alloy with a recrystallized microstructure containing C15 Laves dispersions, which was fabricated via thermomechanical processing (i.e., hot-rolling and annealing), has been reported to show quite high tensile elongation (~7.5%) at room temperature by the present authors [2]. However, the reason for the observed tensile elongation, i.e., whether CoZr phase is inherently ductile or the second phase dispersions of Laves phase are beneficial to ductility to CoZr phase, is not clear at present. In the present study, CoZr ingots with different chemical compositions (Co-49.0Zr, -49.5Zr, -50.0Zr, -50.5Zr and Co-51.0Zr (at.%)) were hot-rolled and subsequently recrystallized to investigate the effect of microstructure on tensile properties and plastic workability.
EXPERIMENT Five kinds of alloys with nominal compositions of Co-49.0Zr, -49.5Zr, -50.0Zr, -50.5Zr and -51.0Zr alloys (at.%) wer
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