Fe-based alloys with high chromium and nickel concentrations are very attractive for efficient energy production in extreme operating conditions. We perform molecular dynamics (MD) simulations of nanoindentation on FCC FeNiCr multicomponent materials. Equiatomic FeNi, Fe55Ni19Cr26, and Fe74Ni8Cr18 are tested by using established interatomic potentials and similar conditions, for the elucidation of key dislocation nucleation mechanisms and interactions. Generally, we find that the presence of Cr in these alloys reduces the mobility of prismatic dislocation loops, and increases their area, regardless of crystallographic orientation. Dislocation nucleation and evolution is tracked during mechanical testing as a function of nanoindentation strain and Kocks-Mecking continuum modeling displays good agreement with MD findings. Furthermore, the analysis of geometrically necessary dislocations (GND) is consistent with the Ma-Clarke’s model at depths lower than 1.5 nm. The presence of Cr leads to a decrease of the GND density with respect to Cr-less FeNi samples, thus we find that Cr is critically responsible of increasing these alloys’ hardness. Post-indentation impression maps indicate that Ni-Fe-Cr compositions display strain localization and hardening due to high Cr concentration.
Alumina (𝛼-Al 2 O 3 ) is one of the major ceramic oxides commonly used for its advanced mechanical properties. Since recently, nanoscale 𝛼-Al 2 O 3 requires more in-depth characterization related to ceramic powder compaction and sintering as well as for applications in the field of biomedical engineering. In this study, we use classical molecular dynamics simulations with a 2/3-body interatomic potential to investigate the mechanical response and the elementary deformation processes of 𝛼-Al 2 O 3 nanoparticles under compression. Resultsshow that 𝛼-Al 2 O 3 nanoparticles resist up to particularly elevated critical force before yielding due to a surface nucleation process including various kinds of dislocations and nanotwins strongly sensitive to orientation and temperature. Results are rationalized in terms of stacking-fault energy and shear stress analysis and are discussed in the light of recent micromechanical tests as well as more fundamental observations performed in the bulk material.
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