Structural evolution and strain induced mixing in Cu–Co composites studied by transmission electron microscopy and atom probe tomography

Abstract

A Cu–Co composite material is chosen as a model system to study structural evolution and phase formations during severe plastic deformation. The evolving microstructures as a function of the applied strain were characterized at the micro-, nano-, and atomic scale-levels by combining scanning electron microscopy and transmission electron microscopy including energy-filtered transmission electron microscopy and electron energy-loss spectroscopy. The amount of intermixing between the two phases at different strains was examined at the atomic scale using atom probe tomography as complimentary method. It is shown that Co particles are dissolved in the Cu matrix during severe plastic deformation to a remarkable extent and their size, number, and volume fraction were quantitatively determined during the deformation process. From the results, it can be concluded that supersaturated solid solutions up to 26 at.% Co in a fcc Cu–26 at.% Co alloy are obtained during deformation. However, the distribution of Co was found to be inhomogeneous even at the highest degree of investigated strain.

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

“…In the studied alloy, large supersaturations up to 26 at.% Co in fcc Cu with an average grain size of 101±20 nm are obtained in the as-deformed state (for further details see Ref. [11]). In comparison with other processing techniques [29][30][31][32][33], the HPT process has certain advantages as the alloying process proceeds in the solid state.…”

“…Although Co shows an extended solubility in Cu after HPT deformation, these solid solutions are not homogenous at the atomic level and Co is enriched in nanometer-sized clusters in the fcc Cu phase even in the as-deformed state (for further details see Ref. [11]]. This is not unexpected since the total free energy decrease immediately after HPT deformation if Co-and Cu-rich regions with small fluctuations in composition are formed.…”

“…Recently, we reported that the formation of supersaturated solid solutions in the Cu-Co alloy system is also feasible by HPT deformation [11]. In the studied alloy, large supersaturations up to 26 at.% Co in fcc Cu with an average grain size of 101±20 nm are obtained in the as-deformed state (for further details see Ref.…”

Evolution of the microstructure of Cu–Fe–Co–Ni powder mixtures upon mechanical alloying

“…The enhancing of mutual solubility of components in Cu-Co binary system during high energy ball milling is also well-known. According to [19][20][21] Cu-Co-alloys can form continuous series of solid solutions, though they are not homogeneous at nanoscale (nanometer-sized clusters of Co still remain in the Cu matrix even after MA at long durations) [22]. Thus, both singleand two-phase structures can be formed in binary systems based on Cu, Fe, Co, Ni elements.…”

High strength nanocrystalline Cu–Co alloys with high tensile ductility

“…The synthesis of novel nanostructured alloys obtained from forced solid solutions in different immiscible systems (i.e., Cu-Ag, Cu-Fe, Cu-Co, Cu-Nb, Mg-Zr, Cu-Ag-Nb, and Ag-Cu-Ni) using high-pressure torsion (HPT) as the bulk processing technique has been the focus of several recent studies. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] These forced solid solutions are not only interesting from a scientific point of view but also for future technical applications. HPTdeformed supersaturated Mg-Zr phases, for example, showed reversible hydrogen storage capability at room temperature.…”