Phase separation of a supersaturated nanocrystalline Cu Co alloy and its influence on thermal stability

TL;DR

This study investigates how phase separation in supersaturated nanocrystalline Cu-Co alloys affects their thermal stability and microstructural evolution during annealing, revealing mechanisms that can tailor nanostructures for property optimization.

Contribution

It provides detailed insights into phase separation mechanisms and microstructural stability of Cu-Co alloys at the nanoscale during thermal treatment.

Findings

Cu-Co alloy remains thermally stable unlike pure Cu and Co.

Phase separation involves spinodal decomposition and larger scale segregation.

Microstructure evolves into pure phases at higher temperatures.

Abstract

The thermal decomposition behavior, the microstructural evolution and its influence on the mechanical properties of a supersaturated Cu Co solid solution with ~100 nm average grain size prepared by severe plastic deformation is investigated under non-isothermal and isothermal annealing conditions. Pure fine grained Cu and Co exhibit substantial grain growth upon annealing, whereas the Cu Co alloy is thermally stable at the same annealing temperatures. The annealed microstructures are studied by independent characterization methods, including scanning electron microscopy, electron energy loss spectroscopy and atom probe tomography. The phase separation process in the Cu Co alloy proceeds by the same mechanism, but on different length scales: a fine scaled spinodal type decomposition is observed in the grain interior, simultaneously Co and Cu regions with a larger scale are formed near the grain boundary regions. Subsequent grain growth at higher annealing temperatures results in a microstructure consisting of the pure equilibrium phases. Such mechanisms can be used to tailor nano structures to optimize certain properties.