Room temperature plasticity and phase transformation of nanometer-sized transition alumina nanoparticles under pressure

Abstract

A powder of transition alumina nanoparticles (including g and a so-called d-type) is compacted at room temperature in a diamond anvil cell (DAC) under pressures ranging from 5 GPa to 20 GPa. Characterization carried out on thin foils prepared by focused ion beam (FIB), from the compacted powder, unambiguously reveals plasticity. High resolution transmission electron microscopy (HRTEM) and electron diffraction also evidence phase transformation of nanoparticles under high pressure and nanoparticles show faceting parallel to the loading direction with a preferential crystallographic orientation of the facets corresponding to {220} planes of gÀAl 2 O 3 . It can also be deduced, from the comparison between the DAC experiments and in situ TEM nano-compression tests on single particles performed in a preceding work, that plasticity is driven by slip bands corresponding to {111} slip planes, common for a spinel structure, such as, for instance, gÀAl 2 O 3 .We also demonstrate that at ambient temperature the transition alumina phase is also prone to structural change under high pressures with the following sequence g-Al 2 O 3 / d * Al 2 O 3 , these two phases coexisting, sometimes, in the same nanoparticle after compaction. Plasticity at room temperature in alumina nanoparticles and the subsequent phase transformation under pressure may have strong impacts on the process of alumina nanostructured ceramics.

Hard-material Adhesion: Which Scales of Roughness Matter?

“…Pull-off calculations using the plastically deformed topography of the sphere were able to accurately reproduce the micronewton scale of pull-off forces from the experimental data. The possibility of plastic flow in similar hard materials has been reported in nanopillars [51] and nanoparticles [52]. A more in-depth analysis of the role of plasticity in these contacts is included in the following section.…”

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60 years of dislocations in ceramics: A conceptual framework for dislocation mechanics in ceramics

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