Grain boundary engineering: historical perspective and future prospects Journal of Materials Science Full Set - Includes `Journal of Materials Science Letters' ISSN 0022-2461 Volume 46 Number 12 J Mater Sci (2011) 46:4095-4115 DOI 10.1007/s10853-011-5393- z 1 23 Your article is protected by copyright and all rights are held exclusively by Springer Science+Business Media, LLC. This e-offprint is for personal use only and shall not be self- archived in electronic repositories. If you wish to self-archive your work, please use the accepted author’s version for posting to your own website or your institution’s repository. You may further deposit the accepted author’s version on a funder’s repository at a funder’s request, provided it is not made publicly available until 12 months after publication. 1 23 Author's personal copy J Mater Sci (2011) 46:4095–4115 DOI 10.1007/s10853-011-5393-z IIB 2010 Grain boundary engineering: historical perspective and future prospects Tadao Watanabe Received: 10 September 2010 / Accepted: 12 February 2011 / Published online: 1 March 2011 Ó Springer Science+Business Media, LLC 2011 Abstract A brief introduction of the historical background demonstrate the presence of large number of grains with of grain boundary engineering for structural and functional various shapes and sizes and the boundaries between the polycrystalline materials is presented herewith. It has been adjoining grains [1], grain boundaries and interphase emphasized that the accumulation of fundamental knowl- boundaries have drawn an increasing attention of materials edge about the structure and properties of grain boundaries scientists and engineers who are deeply involved in materials and interfaces has been extensively done by many design and development. It has now been well established researchers during the past one century. A new approach in that the microstructure is closely related to bulk properties of terms of the concept of grain boundary and interface engi- materials. Accordingly, the control of microstructures has neering is discussed for the design and development of high become one of the key issues of the discipline of Physical performance materials with desirable bulk properties. Metallurgy (earlier) and Materials Science and Engineering Recent advancements based on these concepts clearly (modern). Till date, a large variety of approaches for demonstrate the high potential and general applicability of microstructural control in polycrystalline materials have grain boundary engineering for various kinds of structural been attempted by using the available processing methods. and functional materials. Future prospects of the grain These methods include different metallurgical processes boundary and interface engineering have been outlined, such as solidification, alloying and thermo-mechanical pro- hoping that a new dimension will emerge pertaining to the cessing. Much effort has been made to develop a more pow- discovery of new materials and the generation of a new erful and efficient processing method than the conventional property originating from the presence of grain boundaries ones. There is always a quest to produce such well engi- and interfaces in advanced polycrystalline materials. neered microstructures that can confer desirable bulk prop- erties, mostly in polycrystalline materials, except the case of semiconductors like silicon which are generally single Introduction crystalline, as required by the technological applications. Amongst the past achievements pertaining to the devel- During the past century, our knowledge of interfaces, i.e., opment of newer processing methods, rapid-solidification, grain boundaries and interphase boundaries in crystalline directional solidification, and zone-melting have been solids has enormously developed from a tiny seed to a huge developed in the case of solidification processing. These tree with many branches. Since 1880s, when Sorby first techniques as well as some other recently developed ones are showed the optical micrographs of a blister steel to widely utilized as powerful processing methods of micro- structure control [2–4]. In the past three decades, a number of T. Watanabe (&) new techniques for materials processing have been devel- Key Laboratory of Anisotropy and Texture of Materials, oped and some of them have been successfully applied to the Northeastern University, Shenyang, China production of advanced metallic, semiconductor, and cera- e-mail: [email protected]; [email protected] mic materials by tailoring desirable and stable microstruc- T. Watanabe tures [5]. Amongst these the processing methods, processing Tohoku University, Sendai, Japan under magnetic [6, 7] and electric fields [8] are noteworthy. 123 Author's personal copy 4096 J Mater Sci (2011) 46:4095–4115 On the occasion of the iib2010, it may be useful to briefly have become key to Physical Metallurgy which trans- summarize the previous studies which played important formed to Materials Science and Engineering (MSE) after roles in the historical development of interface science, and 1960s, as reviewed by R. F. Mehl [10] and R. W. Cahn to re-affirm the established concepts. It is also imperative to [11]. A systematic study of the evolution of microstructure mention what needs to be studied further in order to in polycrystalline materials composed of a large variety of strengthen the new discipline of Interface Engineering for grain structures was carefully performed by C. S. Smith in polycrystalline materials with desirable bulk properties and 1940s, to find the key factors controlling grain growth, high performance. In the past three decades, the grain paying particular attention to grain boundaries in single boundary and interface engineering has been extensively phase materials and also inter-phase boundaries in multi- attempted with basic knowledge of grain boundaries and phase alloys [12]. Based on his elaborate effort pertaining interfaces, to improve bulk properties and performance of to experimental observations, it has been revealed that the conventional materials. Moreover, grain boundary and interface energy plays a key role in the evolution of interface engineering may have potential to impact a new microstructure in polycrystalline materials. In 1950s, property and hence, new functions for future advanced probably K.T. Aust and B. Chalmers were amongst the first materials. The present author believes that a brief review of who seriously discussed the relation between energy and important studies of grain boundary-related properties may structure of grain boundaries [13]. The structure of grain be useful for the new comers to know the background as boundaries was first investigated theoretically by Read and well as the recent achievements, and also to specify the Shockley on the basis of dislocation theory [14, 15]. On the milestones leading to the future of Interface Engineering. other hand, optical microscopy of grain boundaries was As discussed by Swalin almost 40 years ago [9], the attempted by Amelinckx through the observation of parti- development of science is generally considered to pass four cle decorating boundaries in transparent crystals such as phases following an S-curve: (i) the first ‘‘Conceptual NaCl for low-angle dislocation boundaries [16]. Hirsch phase’’, is the era when nothing is really known about the et al. [17] applied transmission electron microscopy (TEM) subject. General philosophical principles, that are involved for the observations of dislocation boundaries in deformed to explain observations, grow very slowly in this phase. (ii) aluminum for the first time. Then comes the ‘‘Discovery phase’’, which is a period of The first book on the topic of the structure and properties rapid acceleration. Discoveries are unexpected and thought of grain boundaries and boundary-related phenomena in provoking. In this phase, numerous but conflicting theories polycrystalline materials was written by Donald Mclean in are proposed. The research field seems to be full of puzzles. 1957 [18]. Almost 30 years later, in 1995, Sutton and Many highly motivated scientists enter the field with a Balluffi published their excellent book entitled ‘‘Interfaces hope to achieve notable accomplishments. (iii) The third in Crystalline Materials’’ [19]. The period between 1960s phase is known as ‘‘Breakthrough phase’’. In this phase, the and 1980s can be recognized as the first half of the field makes a rapid progress and becomes fashionable in breakthrough phase in the history of research on grain the leading laboratories. The general pattern of scientific boundaries and interfaces. During this period, a number of events is understood. The field is exciting and rewarding. new concepts on grain boundary structure have been pro- (iv) Ultimately, ‘‘Classical phase’’ sets in, where the posed on the basis of computer simulation and systematic remaining pieces of the jigsaw are put in place. The experimental studies with orientation-controlled bicrystal thought patterns generalized in the breakthrough phase samples, exploring grain boundary structure–property become orthodox and become the conventional wisdom relationship. After 1990s, experimental study of the struc- which must be broken through in the next major advance ture–property relationship of grain boundaries have ultimately leveling off until a new breakthrough occurs. In become possible for polycrystalline samples, because a my personal opinion, the field of grain boundary and computer-assisted and fully automated technique for ori- interfaces