Effect of electric current on nanoindentation of superelastic NiTi alloy

NiTi alloys have many engineering applications in microelectromechanical systems due to their super-elasticity and shape memory effect. Using nanoindentation technique, the effect of DC electric current on the nanoindentation behavior of superelastic NiTi wires with a composition of Ni: 55.8 wt%, Ti: balance, O₂: ≤0.05 wt%, C: ≤0.05 wt% was studied for the current density in a range of 0 to 2.74 kA/cm² and the indentation load in a range of 100 to 1500 μN. The reduced contact modulus increased with increasing electric current density for the current density larger than or equal to 1.32 kA/cm². For the indentation load larger than or equal to 200 μN, the indentation hardness slightly increased with increasing electric current density. The indentation hardness decreased with increasing indentation load, showing the normal indentation size effect. A simple linear relation was derived between the indentation hardness and the square root of the ratio of indentation hardness to indentation load, which is supported by experimental results.