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10/7/03

4:36 PM

Page 2429

Grain-Boundary Character Distribution in Recrystallized L12 Ordered Intermetallic Alloys Y. KANENO and T. TAKASUGI The grain-boundary character distribution (GBCD) of cold-rolled and, subsequently, recrystallized Co3Ti and Ni3(Si,Ti) ordered alloys with an L12 structure was studied by the electron backscattered diffraction (EBSD) method, in association with texture. For comparison, the GBCD of recrystallized pure copper and aluminum was also determined. The recrystallization textures of the Co3Ti alloys as well as the Ni3(Si,Ti) alloy were significantly weak and different from those of the pure copper and aluminum with a strong cube texture. The GBCD of the Co3Ti alloys was characterized by a high frequency of
3 boundaries. On the other hand, the GBCD of the Ni3(Si,Ti) alloy was characterized by a lower frequency of
3 and higher frequency of random (e.g.,
 29) boundaries than that of the Co3Ti alloys. However, the GBCDs of the Co3Ti and Ni3(Si,Ti) alloys were similar to each other and also quite similar to those of the pure copper and aluminum, when
3 boundaries are excluded from the GBCD. Based on these results, the formation mechanism responsible for the recrystallization textures and the grain-boundary structure and energy of the Co3Ti and Ni3(Si,Ti) alloys were discussed, in comparison with those of pure copper and aluminum.

I. INTRODUCTION

THE grain boundary is one of the important metallurgical factors affecting the mechanical, physical, and chemical properties of polycrystalline materials. The grain-boundary structure is often evaluated using a
value, which is defined based on the coincidence-site lattice (CSL) theory.[1] It is well known that grain-boundary properties are strongly dependent on the type and structure of grain boundaries[1] and also that low-
boundaries show high resistance to fracture[2,3] and corrosion.[1,4] Therefore, the grain-boundary character distribution (GBCD) is considered to be a factor used for improving properties of polycrystalline materials. Recent studies concerning the grain-boundary structure focus on the relationship between the GBCD and (crystallographic) texture,[5–10] because most engineering metallic materials, which are usually produced by thermomechanical processing, are textured to a greater or less extent. For instance, the GBCD of conventional metals and alloys such as aluminum,[11,12]. nickel,[13,14] copper,[15,16,17] and iron[18] has been investigated in association with texture. More recently, much attention has been paid to the GBCD of ordered intermetallic alloys. Many ordered intermetallic alloys show high strength, good corrosion resistance, and high phase stability, which make them attractive candidate structural materials for applications at elevated temperatures. However, the room-temperature ductility of ordered intermetallic alloys is generally low because of their complex crystal structures. By extensive efforts carried out during the past two decades, the tensile ductility of L12 ordered intermetallic alloys, wh