SEGREGATION-INDUCED INSTABILITY OF NANOCRYSTALLINE LINE COMPOUNDS

Upon annealing, the stoichiometric nanocrystalline intermetallic compo und Pd3Zr, prepared by high-energy ball milling, simultaneously underg oes grain growth and precipitation of a large fraction of the supersat urated solid solution Pd(Zr); at high annealing temperatures the mater ial transforms back to the single-phase intermetallic state. We presen t an analysis of the thermodynamics of nanocrystalline line compounds, arguing that quite general assumptions fur the material constants of grain boundaries suggest an instability of the overall stoichiometric nanocrystalline compound with respect to precipitation of a second pha se, in accordance with the experimental observation.