Texture evolution and the role of grain boundaries in skeletal formation during coarsening in solid-liquid mixtures
- PDF / 4,856,750 Bytes
- 15 Pages / 612 x 792 pts (letter) Page_size
- 54 Downloads / 196 Views
I. INTRODUCTION
COARSENING is a process by which a multiphase system lowers its total energy by the elimination of interfaces of high curvature. Thus, in a polydisperse solid-liquid system, large particles grow at the expense of small particles. During coarsening in high-volume-fraction solid-liquid mixtures, a so-called skeletal structure is formed in which the solid particles become interconnected, thus potentially altering the coarsening process. There is an ongoing debate over the importance of the solid skeleton in setting the kinetics and mechanisms of the coarsening process. For example, the relative contributions of coalescence and Ostwald ripening to skeletal evolution and particle coarsening in solid-liquid systems has been studied extensively.[1–5] We define coalescence as the nearly instantaneous formation of one large particle upon the contact of two smaller particles. For example, coalescence is believed to increase with the volume fraction of solid due to a concomitant increase in the number of particle-particle contacts.[1,2] Based on an analysis of approximately 20 grain boundaries (GBs) in Cu-Ag using electron channeling patterns, Kaysser et al.[3] suggest that the low-energy GBs needed to allow coalescence may be produced during liquidphase sintering by the formation of favored orientations or by the dissociation of high-energy GBs. In addition, based on an observed decrease in particle contact area with time, German et al. proposed that the relative number of coalescence events is increased by particle rotations into lowenergy misorientations during coarsening.[4] However, Kang and Yoon show that coalescence does not occur in Co-Cu and Fe-Cu alloys, and that the presence of GBs between T.L. WOLFSDORF-BRENNER, formerly with the Department of Materials Science and Engineering, Northwestern University, is a scientist with Kopin Corporation, Taunton, MA. P.W. VOORHEES, Professor, is with the Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208. J. SUTLIFF, Research Scientist, is with General Electric Corporate Research and Development, Schenectady, NY. Manuscript submitted March 17, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS A
two particles does not alter the basic mass-transport process from that of a classical coarsening process.[5] The solid skeleton would, thus, appear to have no major effect on the mechanisms by which coarsening occurs. Therefore, despite the numerous experiments and models on the role of the skeleton in determining the mechanisms and rates of coarsening, the importance of the solid skeleton in the coarsening process remains a matter of great controversy. The skeleton that forms during coarsening is also critical to the success of numerous materials-production techniques. The skeleton plays a significant role in setting properties such as viscosity in semisolid systems.[6] In liquid-phase sintered materials, the skeleton influences the rigidity of the solid-liquid mixture, densification, compact-shape distortion, tensile characteristi
Data Loading...
