Size Effect in the Phase Separation of Cr-W Solid Solutions

Size effects in phase transformations of nanoscale systems show up as significant changes in their phase diagram. Here, using a thermodynamic approach we demonstrate how the immiscibility region of Cr-W solid solutions is influenced by their particle size. For 40- and 70-nm-diameter particles, we consider two thermodynamically stable states with a core-shell configuration, differing in the composition of the core phase. It is shown that, in the nanometer range, one of these states becomes metastable and that the phase diagrams of the stable and metastable states differ significantly. Reducing the particle size leads to a decrease in the upper critical dissolution temperature (UCDP) by 300-400 K and marked changes in the mutual solubility of the components at temperatures comparable to the UCDP.