1997 TMS Annual Meeting: Monday Abstracts

STRUCTURE AND PROPERTIES OF INTERNAL INTERFACES: Session II: Interfacial Kinetics and Motion

Session Chairperson: V. Vitek, Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104

1:30 pm INVITED

GRAIN BOUNDARY MIGRATION EFFECT OF MISORIENTATION, IMPURITIES, PHASE TRANSITIONS AND TRIPLE JUNCTIONS: L.S. Shvindlerman1, G. Gottstein, U. Czubayko, D.A. Molodov, V.G. Sursaeva1, Institut für Metallkunde und Metallphysik, RWTH Aachen, D-52056 Aachen, Germany; 1Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Moscow District, 142432 Russia

The mobility of high-angle grain boundaries and triple junctions is the key factor, which controls the recrystallizations and grain growth processes. The mobility of individual <111> tilt grain boundaries in Al was measured under the constant driving force, in-situ, over a wide range of temperatures, in the vicinity of special misorientation and away from it, in ultra-pure Al and in Al doped with small amount of soluble impurities. The steady state motion of grain boundary systems with triple junctions was investigated in-situ at different temperatures on tricrystals of Zn. A transition of the steady state motion of the grain boundary system with triple junction from junction kinetics to grain boundary kinetics was observed. For the first time it was shown that triple junctions are able to drag grain boundary motion. The grain structure evolution in polycrystals for different kinds of kinetics will be discussed.

2:10 pm

MECHANISMS AND CRYSTALLOGRAPHY OF GRAIN BOUNDARY MIGRATION: A TWO DIMENSIONAL COMPUTER SIMULATION STUDY: M. Upmanyu, R.W. Smith, D.J. Srolovitz, Dept. of Materials Science and Eng., University of Michigan, Ann Arbor, MI 48109

Two dimensional molecular dynamics simulations of grain boundary migration are performed using the half-loop bicrystal geometry employed in the experiments performed by Shvindlerman, et al. We examine the dependence of the steady state grain boundary velocity on grain boundary curvature by varying the half-loop width at constant temperature. The grain boundary velocity is proportional to the half-loop curvature and the grain boundary mobility follows an Arrhenius relationship. In the present study, we examine grain boundary migration for several different grain misorientations. We employ movies of these simulation in order to deduce the dominant mechanisms of grain boundary migration and how these mechanisms depend on grain boundary structure.

2:30 pm

INTERACTION OF SOLUTE SEGREGATION AND GRAIN BOUNDARY SLIDING PROCESSES: J.S. Vetrano, E.P. Simonen, S.M. Bruemmer, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352

The sliding of grain boundaries can be influenced by the presence of solute segregants. Additionally, the sliding mechanism itself also triggers vacancy fluxes that may result in the non-equilibrium redistribution of solute atoms at boundaries and triple points. The interaction of these two processes have been studied in Al Mg-Mn based systems with and without additions of Sn, an equilibrium segregant. Fine-grained structures have been produced and samples tested under conditions that induce grain boundary sliding (GBS). The presence of Sn on the boundaries before deformation allows easier GBS with lower cavitation. High-resolution grain boundary composition measurements on deformed samples revealed that the Sn remains on the boundary during GBS but the Mg is redistributed in a heterogeneous manner. The points to the possibility of engineering the grain boundary composition for optimized deformation characteristics and post-formed properties such as stress corrosion cracking resistance. Work supported by the Materials Division, Office of Basic Energy Sciences, U.S. Department of Energy under Contract DE-AC06-76RLO 1830.

2:50 pm

ATOMISTIC CHARACTERIZATION OF CERAMIC/METAL INTERFACES: SIMULATION AND EXPERIMENTS: D.A. Shashkov, R. Benedek, & D.N. Seidman, Northwestern University, Department of Materials Science and Engineering, Evanston, IL 60208-3108

Our research on ceramic/metal (C/M) interfaces that utilizes transmission electron, high-resolution electron, Z-contrast microscopy, and atom-probe microscopies, in collaboration with ab initio atomistic modeling, is presented. Heavy use is made of atom-probe microscopy to address questions concerning the chemistry of the terminating plane and segregation of solute species to the ceramic/metal interfacial region. Detailed results are presented for the {222} MgO/Cu, {222} CdO/Ag, {222} MgO/Cu(Ag), and {222} CdO/Ag(Au) interfaces. All the C/M interfaces were created via internal oxidation, at elevated temperatures, of high-purity binary or ternary metallic alloys, thereby producing atomically clean interfaces. Solute-atom segregation was induced at the {222} C/M interfaces by annealing specimens containing a ternary addition at 500°C for prolonged periods of time. The level of segregation, i.e., the Gibbsian interfacial excess, is determined directly by the atom-probe technique. Results concerning ab initio atomistic modeling of the {222} MgO/Cu coherent interface (zero-misfit approximation), using local density functional theory (LDFT) within the plane-wave pseudopotential framework, are presented for two polar {111} and two nonpolar {100} MgO/Cu and CdO/Ag interfaces and are discussed with respect to our experimental observations. This research is supported by the Department of Energy/Basic Energy Sciences.

3:10 pm BREAK

3:30 pm INVITED

COMPUTER SIMULATION STUDIES OF THE KINETICS OF INTERFACE DIFFUSION AND PHASE FORMATION: J.M. Rickman, Dept. of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18105-3195

Two kinetic processes associated with grain boundaries are discussed. In the first study, we examine quantitatively the impact of heterogeneous nucleation on the temporal evolution of a phase transformation with particular emphasis on the correlation of nucleation site distribution and product phase microstructure. This is accomplished by investigating spatial correlations in the transforming system via the calculation of nonequilibrium correlation functions and by characterizing product grain sizes and shapes. Computer simulations of transformations are employed in order to validate our theoretical description and to relate microstructural features of the evolving phase to relevant length and time scales in the problem. In the second study, we investigate the kinetics of grain boundary diffusion using a spatially inhomegeneous lattice gasmodel. It is found that atomic transport can be accurately described by a series of approximate rate equations and that one can ascribe a bias, in a certain sense, to tagged atoms.

4:10 pm INVITED

THERMODYNAMICS OF GRAIN BOUNDARY ANISOTROPY AND GRAIN BOUNDARY WETTING: W. Craig Carter, John W. Cahn, Materials Science Engineering Laboratory, NIST, Gaithersburg, MD 20899

Abstract not available.

4:30 pm

MICROCHEMISTRY OF INTERNAL INTERFACES DURING IRRADIATION: E.P. Simonen, S.M. Bruemmer, Pacific Northwest National Laboratory, P.O. Box 999, MS P8-15, Richland, WA 99352

Nonequilibrium microchemistries develop at irradiated interfaces in alloys. The driving force for the radiation-induced segregation is the flow of radiation produced defects to internal interfaces. A unique feature of these segregation profiles is the narrow nanometer dimension near grain boundaries. Theoretical predictions and analytical measurements indicate that nonequilibrium composition gradients normal to grain boundaries are in excess of 106 atom fraction/cm. Fast arrival rates of radiation-produced point defects create potential influences on grain boundary structure and dynamics. Conventional theories assume that dominant mutual recombination of grain boundary defects prevents their influence on boundaries. In the present paper, the dynamics of defect arrival and annihilation are examined in relation to extreme nonequilibrium conditions at internal interfaces. This work was supported by the Materials Sciences Branch, BES, U.S. Department of Energy, under Contract DE-AC06-76RLO 1830.