Nanoscale pseudoelastic behavior of indented titanium-nickel films

The pseudoelastic behavior of shape memory alloy (SMA) materials is a phenomenon associated with reversible thermoelastic martensitic transformation. Despite significant insight into macroscopic pseudoelasticity, relatively little is known about the mechanisms responsible for the pseudoelastic behavior at nanometer scales. Recent demands for powerful microdevices and high-density data storage have motivated SMA film studies. In this study, nanoindentation experiments were performed with sputtered austenite titanium-nickel (TiNi) films using a surface force microscope equipped with an acoustic emission sensor. Results reveal the occurrence of pseudoelasticity at the nanoscale and the significance of normal load, nanoindenter tip radius, and partial unloading on the transition from pseudoelastic to elastic-plastic deformation of the TiNi films. The mechanisms associated with the reversible phase transformation and the energy dissipated in TiNi films exhibiting pseudoelasticity are interpreted in the context of nanoindentation results. The findings of this work demonstrate the high potential of TiNi films in high-density storage and microactuator applications. (C) 2003 American Institute of Physics.