Use of Nanoindentation,Finite Element Simulations,and a Combined Experimental/Numerical Approach to Characterize Elastic Moduli of Individual Porous Silica Particles

This article describes the use of a combination of experimental nanoindentation and finite element numerical simulations to indirectly determine the elastic modulus of individual porous, micron-sized silica (SiO₂) particles. Two independent nanoindentation experiments on individual silica particles were employed, one with a Berkovich pyramidal nanoindenter tip, the other with a flat punch nanoindenter tip. In both cases, 3D finite element simulations were used to generate nanoindenter load–displacement curves for comparison with the corresponding experimental data, using the elastic modulus of the particle as a curve-fitting parameter. The resulting indirectly determined modulus values from the two independent experiments were found to be in good agreement, and were considerably lower than the published values for bulk or particulate solid silica. The results are also consistent with previously reported modulus values for nanoindentation of porous thin film SiO₂. Based on a review of the literature, the authors believe that this is the first article to report on the use of nanoindentation and numerical simulations in a combined experimental/numerical approach to determine the elastic modulus of individual porous silica particles.     

Consolidation of Cu-based amorphous alloy powders by high-pressure torsion

We applied high-pressure torsion (HPT) for consolidation of gas-atomized metallic glass Cu₅₄Zr₂₂Ti₁₈Ni₆ powders into high-density bulk disks. The effects of the number of revolutions (N = 1–5 turns), applied pressure (2.5–10 GPa), and temperature (298–473 K) on densification and structural changes were investigated. The consolidated glassy disks showed an excellent hardness of ~5.2 GPa although a mechanical softening effect along with fragmentation in the center of HPT disks occurred at N > 3 by a couple of branching cracks. The HPT process at higher applied pressures improved the bulk density and inter-particulate bonding, resulting in higher hardness. Increasing the temperature of HPT processing enhanced the densification and deep drawability of the consolidated metallic glass. Although the HPT process did not change the crystallization temperature of the metallic glass powders, it increased the crystallization enthalpy, suggesting the free volume increase and inhibition of a significant nanocrystallization during the HPT process.