Impact of Multiple-Cyclic Nanoindentation on the Mechanical Properties of Copper-Aluminium System

Nanoindentation is widely used for estimating mechanical properties (reduced elastic modulus (E_r) and hardness (H)) of materials at small length scale. In the present work, the focus is to observe the effect of the unloading fraction on E_r and H values for Cu and Cu-Al alloys. Thus, to accomplish this work, single and multiple cycles (partial/complete) indentations are performed where maximum load (P_m) varies from 1000 to 9000 µN and the unloading fraction is varied from 20 to 100%. Our results show that load vs. depth of penetration (P–h) curves follow a similar pattern for single and multiple cycles (partial/complete) indentations. Interestingly, a prominent hysteresis loop is observed in the case of multiple cycle indentation for 80-100% unloading fraction. It is noticed that the loop area increases with the addition of Al atoms due to a higher amount of energy released during unloading, hence it requires more energy during reloading for further plastic deformation. Finally, it is seen that the difference in E_r and H values between single and multiple cycles (partial/complete) indentations is insignificant (± 10%) for all samples. In addition, H values are validated with residual indent impression area acquired for all samples.