A nanocrystalline copper–hafnium alloy by conformal coating powder metallurgy: Microstructure and thermomechanical performance

Abstract

Cu powders, conformally coated with Hf, were used as a precursor for fabricating a bulk Cu–Hf nanocrystalline alloy by mechanical alloying. The resultant specimens were plastically deformed at ambient and elevated temperatures. The Cu matrix is nanocrystalline and contains a nanoscale, monoclinic HfO2 precipitate dispersion. Despite the plastic deformation, the microstructure did not coarsen. However, the alloy began accommodating deformation by grain boundary mechanisms at much lower temperatures than other stabilized, nanocrystalline Cu-based alloys. This behavior is attributed to the incoherency of the HfO2 precipitates with the Cu matrix, highlighting the importance of coherency of the stabilizing precipitate with the matrix as well as the phase change(s) that stabilizing solutes may have in the presence of contaminates.