Microstructural evolution in cu-spinodal alloy driven by high-energy ball milling and dry sliding wear

We report on the microstructural and phase evolution of a Cu-15wt%Ni-8wt%Sn alloy that is subjected to sustained plastic deformation, either by high-energy ball milling or during dry sliding wear testing. This bronze, which is designated as C72900, can be hardened by spinodal decomposition and used in high performance bearings. Microstructural characterization of the ball milled powders and of the wear debris reveals that sustained plastic deformation, through forced mixing of the chemical species, has transformed the initial spinodal structure into an fee solid solution. Transmission electron microscopy shows also that these materials have developed small grain sizes, ranging from 20 to 200nm, with a rather pronounced texture in the ball milled powders. High resolution TEM imaging makes it possible to identify dislocations, sub-grain boundaries and nanotwins. Pin-on-disc wear tests reveal the existence of a transition from mild wear to severe wear as the load is increased. It is proposed that this transition may be affected by the microstructural changes forced in the transfer layer by sustained plastic deformation, in particular the destabilization of the initial spinodal structure.