Plastic Deformation of Al0.3CoCrFeNi and AlCoCrFeNi High-Entropy Alloys Under Nanoindentation

The mechanical properties of Al0.3CoCrFeNi and AlCoCrFeNi high-entropy alloys (HEAs) were investigated by instrumented nanoindentation over a broad range of loading rates. It was found that the loading portion of the two HEAs exhibited apparent discontinuities at low loading rates. However, the discontinuity became less pronounced with increasing the loading rate. The experimental results that the hardness, elastic modulus, and yield strength of AlCoCrFeNi HEAs are larger than those of Al0.3CoCrFeNi HEAs can be elucidated in terms of thermodynamic and topological parameters of the constituent elements and solid solution strengthening, respectively. In situ scanning images displayed a significant pile-up around the indents, demonstrating that a highly localized plastic deformation occurred under nanoindentation. Furthermore, the resistance for creep behavior increases as the Al concentration is increased due to the enlarged lattice distortion related to a solution strengthening effect.