Tribological Behavior of Microalloyed Cu50Zr50 Alloy

Abstract

Promoting the martensitic transformation through optimum microalloying with Fe and/or Mn was observed to be an effective method to enhance the wear resistance of the Cu₅₀Zr₅₀ at. % shape memory alloy (SMA). Among all the potential microelements and concentrations, partial replacement of Cu by up to 1 at. % Fe and Mn is of interest since from density functional based calculations large minimization of the stacking fault energy (SFE) of the B2 CuZr phase is predicted. For this reason, an effective martensitic transformation is expected. The largest decrease of the SFE from 0.36 J/m² to 0.26 J/m² is achieved with partial replacement of Cu by 0.5 at. % Fe. This results in the highest martensitic transformation upon wear testing, especially at highest load (15 N) for which the mass loss is 0.0123 g compared to 0.0177 g for Cu₅₀Zr₅₀ and a specific wear rate of 5.9 mm³/Nm, compared to 8.5 for mm³/Nm for Cu₅₀Zr₅₀. This agrees with the low coefficient of friction of 0.48±0.05 and low roughness of 0.200±0.013 μm of the Fe-containing alloy compared to that for Cu₅₀Zr₅₀, 0.55 and 0.415±0.026 μm, respectively. All the worn surfaces show the formation of abrasive grooves, being shallowest for the more wear resistant 0.5 at. % Fe alloy. The second more wear resistant alloy contains 0.5 at. % Mn. Wear mechanisms of abrasion, adhesion and delamination have been identified.