In this article, for the first time, in situ and real-time experimental observations of changes in solid/liquid (s/l) interface shape during interactions with a particle or void are reported for metallic systems. Real-time interface shape evolution for both stationary and growing interfaces was observed by use of a state-of-the-art X-ray transmission microscope. Localized interfacial perturbations were studied as a function of the particle or void diameter, the distance between the s/l interface and the particle or void, and the thermal conductivity ratio between the matrix and the particle or void. In particular, the sensitivity of interfacial perturbation to the thermal conductivity ratio is critically analyzed. Analytical predictions of interface shape are compared to the real-time, in situ experimental data. A good agreement between the experimentally observed and predicted interface shapes was found for stationary interfaces. Based on the differences in experimental observations, between a moving and a stationary interface, an alternate hypothesis is suggested to explain the observed kinetics of particle engulfment by a growing interface.

Fundamental limitations, with respect to nanocrystalline materials, of the traditional elaboration of powder diffraction data like the Rietveld method are discussed. A tentative method of the analysis of powder diffraction patterns of nanocrystals based on the examination of the variation of lattice parameters calculated from individual Bragg lines (named the “

Results of the directional solidification (DS) experiments on particle engulfment and pushing by solidifying interfaces (PEP), conducted on the space shuttle Columbia during the Life and Microgravity Science (LMS) Mission, are reported. Two pure aluminum (99.999 pct) 9 mm cylindrical rods, loaded with about 2 vol pct 500-m-diameter zirconia particles, were melted and resolidified in the microgravity (g) environment of the shuttle. One sample was processed at a stepwise increased solidification velocity and the other at a stepwise decreased velocity. It was found that a pushing/engulfment transition (PET) occurred in the velocity range of 0.5 to 1 m/s. This is smaller than the ground PET velocity of 1.9 to 2.4 m/s. This demonstrates that natural convection increases the critical velocity. A previously proposed analytical model for PEP was further developed. A major effort to identify and produce data for the surface energy of various interfaces required for calculation was undertaken. The predicted critical velocity for PET was 0.775 m/s.

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Directional solidification experiments have been carried out to determine the pushing/engulfment transition for two different metal/particle systems. The systems chosen were aluminum/zirconia particles and zinc/zirconia particles. Pure metals (99.999 pct Al and 99.95 pct Zn) and spherical particles (500 m in diameter) were used. The particles were nonreactive with the matrices within the temperature range of interest. The experiments were conducted so as to ensure a planar solid/liquid (SL) interface during solidification. Particle location before and after processing was evaluated by X-ray transmission microscopy (XTM) for the Al/ZrO 2 samples. All samples were characterized by optical metallography after processing. A clear methodology for the experiment evaluation was developed to unambiguously interpret the occurrence of the pushing/engulfment transition (PET). It was found that the critical velocity for engulfment ranges from 1.9 to 2.4 m/s for Al/ZrO 2 and from 1.9 to 2.9 m/s for Zn/ZrO 2 .