Materials Week '97: Monday AM Session

Focusing on physical metallurgy and materials, Materials Week '97, which incorporates the TMS Fall Meeting, features a wide array of technical symposia sponsored by The Minerals, Metals & Materials Society (TMS) and ASM International. The meeting will be held September 14-18 in Indianapolis, Indiana. The following session will be held Monday morning, September 15.

BOUNDARIES AND INTERFACES IN MATERIALS: THE DAVID A. SMITH SYMPOSIUM: Session I

Session Chair: William A.T. Clark, The Ohio State University, Columbus, OH 43210

OPENING REMARKS: David B. Williams, Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015

8:35 am INVITED

MICROSTRUCTURAL DESIGN AND TAILORING OF ADVANCED MATERIALS: Gareth Thomas, Department of Materials Science, University of California, 561Evans Hall, Berkeley, CA 94720

We live and work in a world that depends on materials and their performance. The science of metallurgy and its extension to materials in general has arrived over the past 50 years at a position of great understanding, so much so that we can now tailor the desired microstructure for scientific properties using appropriate processing and controls. From a scientific approach to materials technology, the relationships between processing, structures and performance must continue to be established. This is the main task for materials scientists. Progress in experimentation and instrumentation has been truly remarkable these past 50 years - we can even image columns of atoms and do atom-by-atom spectroscopy! The electron microscope with all its modern capabilities for high resolution imaging, diffraction and spectroscopy remains central to our means of understanding the relationships between structure and composition. It will be the focus of this lecture to discuss present limitations of high resolution TEM and to draw upon examples of the role microscopy plays in materials engineering. In almost all cases, the problems relate to interfaces. Examples include development of cold formable, corrosion resistant low-carbon dual phase steels for concrete reinforcement; structural and electronic ceramics (including a new approach to joining high temperature ceramics); and a wide range of magnetic materials, involving nanostructures.

9:00 am INVITED

GRAIN BOUNDARY ARCHITECTURE FOR HIGH PERFORMANCE MATERIALS: T. Watanabe, Laboratory of Materials Design and Interface Engineering, Faculty of Engineering, Tohoku University, Sendai, Japan

Grain boundaries are important microstructural elements and a source of high-performance in polycrystalline materials. Because of their structural and configurational versatility and flexibility, grain boundaries can produce a large variety of effects on bulk properties of materials. The concept of "Grain Boundary Design and Control for High-Performance Materials" was proposed in 1984 on the basis of the relationship between grain boundary structure and properties. A new microstructural factor termed "Grain Boundary Character Distribution (GBCD)" has been introduced. The manipulation of GBCD and other factors enables us to design and develop high performance materials by controlling detrimental effects and by enhancing their beneficial grain boundaries. The concept has been proved to be applicable and powerful in designing and producing high-performance materials in connection with processing. An overview of recent achievements of Grain Boundary Architecture and prospect for the future will be given.

9:30 am INVITED

THERMAL PROPERTIES OF NANOSTRUCTURED MATERIALS: U. Erb, T. Turi¹, B. Szpunar⁺, G. Palumbo² and K.T. Aust, Department of Metallurgy and Materials Science, University of Toronto, Toronto, Canada M5S 3E4; ¹Department of Materials and Metallurgical Engineering, Queen's University, Kingston, Ontario, Canada K7L 3N6; ²Ontario Hydro Technologies, 800 Kipling Avenue, Toronto, Canada M8Z 5S4

The effect of grain boundary volume fraction on thermal expansion, specific heat, diffusion, and thermal stability of fully dense nanstructured materials produced by electrodeposition will be presented. This will be followed by a comparison with property measurements performed on materials produced by other synthesis methods. The variation in properties observed for materials produced by various synthesis methods will be discussed in terms of microstructural differences (i.e. grain boundary structure, porosity, impurity content, texture).

10:00 am BREAK

10:10 am INVITED

GRAIN BOUNDARY STRUCTURE IN NON-CUBIC CRYSTAL SYSTEMS: R.C. Pond, F. Sarrazit, M. Aindow*, Department of Materials Science and Engineering, University of Liverpool, Liverpool L69 3BX, UK; *School of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

Currently, the most widely accepted model of interfacial structure is based on the notion of reference configurations, which exhibit low free energy, and where any additional angular deviation and/or misfit present is accommodated by arrays of interfacial defects. This model has been extensively validated for the cubic crystal system, but further considerations may be necessary in other cases. This is illustrated in the present paper by experimental observations, using transmission electron microscopy, of interfaces in -Ti and ZnO. In the latter case, for example, a transition was observed from a facetted interfacial structure consistent with the above model to an alternative planar form based on a reference structure which was quasicrystalline in one dimension.

10:40 am

A GEOMETRIC CRITERION FOR "SPECIAL" CSL GRAIN BOUNDARY PROPERTIES: G. Palumbo^1,2 K.T. Aust², E.M. Lehockey¹, U. Erb², P. Lin¹, ¹Ontario Hydro Technologies, 800 Kipling Avenue, Toronto, Canada M8Z 5S4; ²Department of Metallurgy and Materials Science, University of Toronto, Toronto, Canada M5S 3E4

Although widely used for the characterization of grain boundaries within the coincidence site lattice (CSL) framework, the application of Brandon's criterion (for allowable angular deviation), has often resulted in grain boundaries which do not display "special" behavior being classified as low S CSL's; thus prompting some debate as to the overall validity of the CSL model. In this present work, the crystallographic basis for a previously formulated, more restrictive criterion for "special" boundaries is presented. The applicability of this criterion is shown to be supported by (1) a review of TEM evidence for the resolution of discrete intrinsic grain boundary dislocations, and (2) relative grain boundary performance in numerous experiments for corrosion, cracking, and creep cavitation susceptibility of several pure metals and commercial alloys.

11:00 am

RODRIGUES-FRANK MAPPING OF INTERFACE CRYSTALLOGRAPHY: Krishna Rajan, Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180-3590

The utility of Rodrigues-Frank vectors in crystallographically representing grain boundary misorientation will be described in this presentation. It will be shown that Rodrigues-Frank (R-F) mapping of microstructures is in fact well suited to experimental techniques which characterize grain specific orientation. R-F representations also permit the coupling of grain boundary misorientation associated with crystal symmetry to issues associated with sample symmetry. The value of such representations in problems ranging from deformation processing to thin film growth will be discussed.

11:20 am

ENGINEERING OF GRAIN BOUNDARIES IN LEAD ALLOYS FOR IMPROVED Pb-ACID BATTERY PERFORMANCE: E.M. Lehockey, G. Palumbo, A.M. Brennenstuhl, P. Lin, Ontario Hydro Technologies, 800 Kipling Avenue, Toronto, Canada M8Z 5S4

Lead-acid battery life is limited by intergranular degradation of the Pb alloy electrodes, including: corrosion (grain dropping), cracking, and grain boundary sliding (creep). Efforts to improve the resistance of the electrodes to these effects have focused on altering the microstructure to contain high frequencies of grain boundaries at/near low-S CSL misorientations. Elevating the frequency of these "special" interfaces from 12% in conventional material to 60% reduces weight loss (corrosion) and growth (creep) of PbCaSn electrodes, measured in industry standard tests, by 30% and 70% respectively. Similar processing increases the number of charge-discharge cycles to failure in PbSb alloy electrodes by 5-fold, arising from crack blunting at low-S CSL boundaries. These results clearly advocate a role for "grain boundary engineering" in developing advanced stationary and SLI batteries with superior reliability and energy density.

11:40 am

EVOLUTION OF THE FCC/L1₂ INTERFACE DURING DIFFUSION-BONDING: K. Fujiwara, Y. Ootoshi, Z. Horita, M. Nemoto, Department of Materials Science and Engineering, Faculty of Engineering 36, Kyushu University, Fukuoka 812-81, Japan

This study presents diffusion-couple experiments where Ni is bonded with Ni-based intermetallics having an L1₂-type crystal structure such as Ni₃X (X=Al, Si, Ga and Ge). Microstructural observations and selected area electron diffraction analyses have revealed that the Ni-rich solid solution phase (-phase) grows towards the intermetallic phase (-phase) during diffusion bonding. There exists an identical orientation relationship between the and phases when the annealing is conducted at higher temperatures but no such relationship is present when the couple is annealed at lower temperatures. It is then suggested that there is a critical temperature for the presence of the identical orientation relationship between the and phases. The critical temperature depends on the types of diffusion-couples and it appears that the lattice misfit is an important factor in determining the critical temperature.

12:00 pm INVITED

THE STRUCTURE OF NON-SPECIAL BOUNDARIES IN ALUMINUM: C.L. Briant, R. Bai, R. Phillips, V. Shinoy, A. Schwartzman, Division of Engineering, Brown University, Providence, RI 02912

Most studies of the structure of grain boundaries in metals have focused on special boundaries that have a high number of coincident lattice sites. Although these studies have yielded extremely valuable information, these boundaries are not the ones most often encountered in engineering practice. In this work we report on the structure of grain boundaries that are non-special in their orientation. Tilt boundaries of aluminum were prepared either by strain annealing or by growing bi-crystals from the melt. High resolution transmission electron microscopy images of these boundaries were obtained; all boundaries were of the <110> type. The structures of these boundaries were determined by high resolution TEM and were compared with structures simulated by the quasi-continuum method. The results of these studies will be discussed in terms of different grain boundary structure models. A discussion will also be presented on the use of the quasi-continuum method to simulate both the motion of grain boundaries and the response of grain boundaries to a mechanical stress. This work was sponsored by DOE contract DE-FG02-96ER45578.