Abstract
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.
Highlights
Shape memory alloys (SMAs) have been extensively investigated over the years due to their interesting mechanical properties [1, 2]
The Fe0.5 plot does not lie between Fe1 and Fe0 because partial replacement of Cu in B2 CuZr by 0.5 at. % Fe decreases the stacking fault energy (SFE) of Fe0 the largest (i.e., minimum energy (J/m2))
For Fe0.5, the shallow grooves indicate the lowest wear volume and lowest wear rate, which agrees with the lowest mass loss values (Fig. 5)
Summary
Shape memory alloys (SMAs) have been extensively investigated over the years due to their interesting mechanical properties [1, 2]. An effective method to tune the performance of Cu-Zr SMAs is to promote the presence of microalloying elements in solid solution inside austenite by using rapid solidification and prevent their segregation to the grain boundaries [8] This is of interest since the retention of elements in small concentrations inside the crystalline lattice of B2 CuZr austenite can alter its Stacking Fault Energy (SFE) [9]. Higher cooling rate results in finer microstructures [16], which can be useful to prevent embrittlement of CuZr based SMAs since these alloys become brittle when the Cu grains are large [17, 8] This effect is attributed to intergranular cracking mostly caused by high elastic anisotropy [18]. The effect of minor Fe and Mn additions on the wear performance of CuZr by using both experimental and computational techniques will be used
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