Nanoscale characterization of the transfer layer formed during dry sliding of Cu–15 wt.% Ni–8 wt.% Sn bronze alloy

The microstructure of the transfer layer, and the underlying severely plastically deformed layer (SPDL), formed during the dry sliding of a spinodally hardened Cu–15 wt.% Ni–8 wt.% Sn bronze against a stainless steel, is characterized at the nanoscale by conventional and analytical transmission electron microscopy, including energy-dispersive spectroscopy and electron energy loss spectroscopy. The SPDL consists of a Cu–Ni–Sn solid solution with elongated nanograins, due to extensive dislocation glide and twinning. In contrast, the transfer layer, 2–3 μm thick, is an equiaxed nanocomposite comprised of a Cu-rich metallic phase with a (Fe,Cr)2O3-based oxide precipitates, and forms as a result of the mechanical mixing and compaction of wear debris. The bronze in this layer has undergone dealloying, indicative of the importance of thermal effects. The dispersion of oxide in the transfer layer suggests a different type of forced mixing, possibly turbulent mixing. The transfer layer is observed to improve significantly the wear resistance of the bronze.