Special Topic: Ultrafine‐Grained Materials

Ultrafine-grained (UFG) materials with uniform microstructures in the 100 nm – 1 µm range are attractive for many applications because of their substantially improved mechanical properties as compared to conventional materials. However, the limited understanding of the mechanisms governing the mechanical behavior and the lack of validated models have been the key roadblocks to the widespread use of these materials. Thus, in 2004 a research unit entitled “Mechanische Eigenschaften und Grenzflächen ultrafeinkörniger Werkstoffe” was established by Deutsche Forschungsgemeinschaft (DFG) to address these issues with the ultimate goal of bridging the gap between basic research and engineering applications. In this joint effort various materials were studied and different characterization and testing techniques were combined in order to establish a thorough understanding of the microstructure-property relationships in UFG materials and develop microstructure-based models that allow for prediction of the behavior of these materials. Part of the results obtained was presented during the closing event of the DFG research unit at the MSE-2010 congress in Darmstadt. The present issue of Advanced Engineering Materials features eight full papers, which address different aspects relevant for UFG materials. The papers were selected and arranged such as to cover the complete chain from processing to characterization to modeling. The first study focuses on different processing methods for UFG materials and discusses the influence on the resulting microstructure. As the type of interfaces present in the microstructure is a dominant parameter in UFG materials, the grain boundary character distribution is analyzed in 3D in the second paper. Another paramount issue in UFG materials is stability of the microstructure established during processing, and the thermal stability is addressed in the next article. UFG materials also demonstrate enhanced strain rate sensitivity, and data obtained on different scales are presented in the fourth paper. UFG microstructures not only enhance the mechanical properties of structural materials, but a reduction in grain size can also be exploited to improve the cyclic stability of functional materials as demonstrated in the following study. In fact, cyclic stability is a property that can be controlled efficiently by adjusting the UFG microstructure as detailed by the next two papers. Finally, the last study in this series makes use of different experimental data sets and presents a model that addresses the interaction between dislocations and different grain boundaries in UFG materials. Clearly, this joint research would not have been possible without the continued financial support of DFG, which is gratefully acknowledged. We wish you an enjoyable read and hope that the papers included in this issue will stimulate future research in the field.