Materials Science and Engineering, A 166 (1993) 237-241 237 Future research directions for interface engineering in high temperature plasticity T. G. Langdon Departments of Materials Science and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089-1453 (USA) T. Watanabe Department of Materials Science, Faculty of Engineering, Tohoku University, Sendai 980 (Japan) J. Wadsworth Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94551 (USA) M. J. Mayo Department of Material Science and Engineering, Pennsylvania State University, University Park, PA 16802 (USA) S. R. Nutt Division of Engineering, Brown University, Providence, RI 02912 (USA) M. E. Kassner Department of Mechanical Engineering, Oregon State University, Corvallis, OR 97331-6001 (USA) Abstract This paper summarizes briefly some of the conclusions arising from the workshop on Grain Boundary and Interface Phenomena in the High Temperature Plasticityof Solids and outlines possible directions for future research. 1. Introduction The workshop on Grain Boundary and Interface Phenomena in the High Temperature Plasticity of Solids provided strong confirmation of the validity of combining apparently diverse fields within the broad framework of interface engineering. In order to consider future research directions, it is useful initially to examine the use of grain boundary design as it applies to polycrystalline metals and ceramics, and then to consider separately the problems associated with three classes of materials where inter- face phenomena are often the dominant factor in deter- mining the nature of high temperature plasticity: superplastic materials, nanocrystaUine materials and composite materials. 2. Grain boundary design Using high resolution electron microscopy on bi- crystals with well characterized grain boundaries, it has been possible in recent years to make rapid progress in evaluating the atomistic structure and properties of grain boundaries and interphase boundaries (including heterophase interfaces between dissimilar materials). As a result of these studies, it is known that grain boundaries and interfaces have substantial structural variability and exhibit significant differences in their properties. It is now well established that the properties of grain and interphase boundaries depend strongly on the precise type and structure of the boundaries. Until recently, it was usual to consider the influence of grain boundaries in terms of their geometrical aspects, such as grain size (i.e. grain boundary density) and grain boundary inclination; an example is unidirectionally boundary-aligned materials produced by solidification. Thus, the role of boundary structure was generally not included. An important current problem is bridging the gap between the structure-dependent properties of indi- vidual boundaries and the boundary-related bulk properties of a polycrystal. A new microstructural parameter has been introduced, termed the grain 0921-5093/93/$6.00 © 1993 - Elsevier Sequoia. All rights reserved