P. C. King, S. H. Zahiri, M. Jahedi, CSIRO, Clayton, Australia
The microstructural alterations in 99.7 wt% copper powder during cold spray were investigated. A highly non-homogeneous microstructure resulted due to the variety of thermomechanical conditions produced during deformation of the particles. Large strains and high strain rates resulted in significant grain refinement and the formation of sub-100 nanometre grains. Deformation occurred by slip and twinning, the latter promoted by impurities in the copper feedstock. Heating of the deposit by the impinging gas jet also resulted in recrystallisation. Thin foils from the deposits were studied by transmission electron microscopy (TEM). Cross-sections of single deformed particles were made using a focussed ion beam / scanning electron microscope (FIB/SEM).
Summary: The development of nanocrystalline structures in cold sprayed copper is described. Deformation twinning, formation of sub-100nm grains and recrystallisation were related to the thermomechanical history of deposit formation.
