Tuning the tribological performance of Cu50Zr50 through microalloying

It was observed from pin-on-disc tests that microalloying with Fe and/or Mn is an effective method to enhance the wear resistance of Cu50Zr50 at. % shape memory alloy (SMA) because these elements can promote the martensitic transformation when they are present in certain concentrations. The microstructure of Cu50Zr50 at. % SMA mostly consists of B2 CuZr and partial replacement of Cu by up to 1 at. % Fe and Mn is of interest because they can decrease the stacking fault energy (SFE) of B2 CuZr according to density functional based calculations. A decrease in the SFE means a more effective martensitic transformation. When Cu is partially replaced by 0.5 at. % Fe, there is a decrease of the SFE, from 0.36 J/m2 to 0.26 J/m2, and therefore the highest martensitic transformation upon wear testing is achieved. This results in the highest wear resistance of the Cu50Zr50 at. % SMA, especially for 15 N load, for which the mass loss decreases from 0.0177 g to 0.0123 g. These results are consistent with the low roughness, 0.1870.23 μm, and coefficient of friction, 0.48, obtained when Cu is partially replaced by Fe compared to the values for Cu50Zr50, 0.55 and 0.4510.59 μm, respectively. Observation of the worn surfaces suggest that the more wear resistant alloy is the one containing 0.5 at. % Fe, since the abrasive grooves are the swallowest while the alloy with 0.5 at. % Mn is the second more wear resistant, for which the surface roughness is 0.3010.38 μm. Sliding wear tests on SS304 counterbody indicate that the wear mechanisms are abrasion, adhesion and delamination.