Antimony-induced embrittlement of [011] symmetric tilt boundaries in copper bicrystals
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I. INTRODUCTION
IT is well known that intergranular fracture behavior of solids induced by segregates depends strongly on the grainboundary structure. Many investigations have attributed the structural dependence to the tendency of impurity atoms to segregate at various levels to individual grain boundaries.[1] The segregation of Sb on grain boundaries in Cu also results in embrittlement. However, few experiments have been reported on the Sb-induced boundary embrittlement. Hopkin[2] carried out impact tests and tensile tests on polycrystals of Cu alloys containing 1.7 and 2.0 wt pct Sb between 4 and 773 K, and showed that these alloys suffered from intergranular brittleness at both low and high temperatures, but that at some intermediate temperatures they were more ductile. That is, plots of energy to produce failure against temperature had well-defined peaks. Chuang et al.[3] measured the enrichment ratio of Sb at intergranular fracture surfaces in Cu-0.96 wt pct Sb bicrystals for four kinds of [011] symmetric tilt boundaries by Auger electron microscopy, and showed that, for a given segregation heat treatment, the fracture mode of these bicrystals depended on the misorientation angle and corresponded well to the amount of Sb segregation. On the other hand, many investigators have studied the dependence of the grain-boundary embrittlement of Cu by an addition of a small amount of Bi on the grain-boundary character.[4–10] Roy et al.[4] examined the Bi-induced boundary embrittlement in Cu as a function of the atomic structure of boundaries and showed that least embrittled boundaries were the boundaries of least energies after Bi doping. On the other hand, Miura et al. investigated systematically the embrittlement of Bi-added Cu bicrystals with various [011][6] and [001][7] symmetric tilt grain boundaries. For both types of grain boundaries, they found that the bicrystals be-
R. MONZEN, Professor, and T. KUZE and O. MATSUDA, Graduate Students, are with the Department of Mechanical Systems Engineering, Kanazawa University, Kanazawa 920-8667, Japan. Contact e-mail: [email protected] H. MIURA, Associate Professor, is with the Department of Mechanical Engineering and Intelligent Systems, The University of Electro-Communications, Tokyo 182-8585, Japan. Manuscript submitted June 11, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS A
came more brittle as the energy of grain boundaries of pure Cu increases. Monzen et al.[10] conducted a similar study for [011] twist boundaries and found that the degree of embrittlement of a boundary showed a good correlation with the energy of the boundary before Bi doping. In the present work, Cu bicrystals with different [011] symmetric tilt boundaries doped with Sb were tensile tested between 77 and 773 K. The correlation between the grainboundary embrittlement and their energy before and after Sb doping will be examined. Miura et al.[11] have already measured the energies of [011] symmetric tilt boundaries of pure Cu with sufficient accuracy using a method of shape analysis of grain-bou
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