Maja Krcmar

A comparative first-principles study of martensitic phase transformations in TiPd2 and TiPd intermetallics.

The recent synthesis and characterization of bilayers of vitreous silica has produced valuable new information on ring sizes and distributions. In this paper, we compare the ring statistics of experimental samples with computer generated samples. The average ring size is fixed at six by topology, but the width, skewness and other moments of the distribution of ring edges are characteristics of particular samples. We examine the Aboav-Weaire law that quantifies the propensity of smaller rings to be adjacent to larger rings, and find similar results for available experimental samples which however differ somewhat from computer-generated bilayers currently. We introduce a new law for the areas of rings of various sizes.

Structural transformations and improved ductility in ordered FeCo and ZrCo intermetallics

Using the first-principles calculations, we find that Fe-Co has a tendency for a structural transformation to a lower symmetry sheared L10 phase under the applied shear stresses. This tendency for structural transformation can have a significant influence on the mechanical properties of FeCo, as it might be closely connected with the intrinsic brittleness of Fe-rich and stoichiometric FeCo alloys and with the improved ductility of Co-rich FeCo alloys. We suggest that improved ductility in Co-rich FeCo alloys may originate from transformation toughening due to the B2→L1 0 structural transformation near the regions of high stress concentration, as the stress energy is fully dissipated by the decrease in the electronic energy due to the structural phase transformation into a lower energy structure. Similarly, in ZrCo, our first-principles calculations find that a B2→B33 martensitic phase transformation can occur under the applied shear stress, which may contribute to the good ductility of this alloy, despite the fact that ZrCo is a strongly ordered line compound.

First-Principles Study of Structural and Defect Properties in FeCo Intermetallics

Employing ab-initio calculations and statistical thermodynamic modeling, we investigated the structural stability, defect energies, and ordering of B2 FeCo intermetallics. We find that FeCo in the B2 structure is a marginally stable and weakly ordered system, with a high density of antisite defects on both sublattices and low APB energies for the slip on both {l_brace}110{r_brace} and {l_brace}112{r_brace} planes. The structural stability of B2 FeCo is very sensitive to the change in local atomic environment, as the system transforms to a lower-symmetry L10 phase under the effects of reduced dimensionality or applied shear stress. We suggest that internal stresses near dislocation cores might be closely connected with the intrinsic brittleness of ordered FeCo, as it is likely to induce a local structural transformation from the B2 structure to the L10 structure.