Description:

Dr. Maria Gandman
Department of Materials Science and Engineering
University of California, Berkeley

Abstract
Metal-ceramic systems are important in fundamental science as well as in various technological applications. The metal-ceramic interfaces play crucial role in thermal and mechanical stability of those systems and often affect the properties of metal-ceramic systems desired for engineering applications. In this talk, investigations of solid-liquid and solid-solid metal-ceramic interfaces will be presented.

In the first part of the talk, ordering in liquid Al adjacent to various terminating planes of crystalline α-alumina will be presented. Experiments were conducted using two techniques: in-situ aberration-corrected high resolution transmission electron microscopy (HRTEM) and in-situ electron energy loss spectroscopy (EELS). Heating experiments were conducted using a monochromated and spherical aberration (Cs) corrected FEI Titan 80-300 S/TEM. The use of Cs corrected HRTEM enabled direct and quantitative analysis of the ordering phenomenon at different terminating alumina facets. The energy of Al bulk plasmons was found to be sensitive to local ordering of the liquid at the interface with alumina, which provided a second independent method for the quantification of structural ordering by in situ EELS. Comparison of the data obtained from in situ EELS with the results from Cs-corrected HRTEM provided information regarding preferential oxygen segregation to the ordered liquid at different alumina facets [1,2].

In the second part of the talk, a model system of Pt-implanted polycrystalline alumina used for investigating the equilibration kinetics of metal inclusions in a ceramic matrix will be presented. The system was annealed at 1565°C promoting grain-growth of the polycrystalline alumina. Upon annealing in air, the implanted Pt+ ions coalesced into metal inclusions, and were consequently swept by growing α-alumina. This sequence of events enabled the investigation of Pt shape-equilibration kinetics. The Pt particles occluded in the α-alumina grains found in different stages of re-equilibration with the new alumina orientations were investigated by HRTEM and HRSTEM. The mobility of Pt particles was found to differ as a function of the moving alumina grain-boundary plane. Large amounts of differently oriented alumina grains that grow during annealing enable the investigation of metastable equilibrium states of Pt particles, which are forced to re-orient in accordance with newly imposed, host alumina grains. Those metastable states provide valuable information regarding relative energies of Pt-alumina interfaces not usually present under global equilibrium conditions. Study of metal-ceramic interfaces not present in the equilibrium (Wulff) shape enables the determination of the necessary conditions (in terms of the ceramic grain orientations) for stabilization of metastable metal-ceramic orientation relationships [3].

References
1. M. Gandman, Y. Kauffmann, C. T. Koch, and W. D. Kaplan, Physical Review Letters 110, 086106 (2013).
2. M. Gandman, Y. Kauffmann, and W. D. Kaplan, Applied Physics Letters 106, 051603 (2015).
3. M. Gandman, M. Ridgway, R. Gronsky, and A. M. Glaeser, Acta Materialia 83, 169 (2015).