Nanoindenter Tip Research Articles

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.

Apparent indentation size effect in a CVD aluminide coated Ni-base superalloy

Indentation hardness testing was used to assess the mechanical properties of a low activity CVD β-NiAl bond coat applied to a single crystal Ni-base superalloy substrate. Tests performed in the nano- and micro-hardness regimes using a Knoop indenter geometry revealed the presence of an indentation size effect (ISE) where the apparent hardness increased significantly with decreasing indentation test load. An energy balance analysis was applied to analyze the apparent ISE and to extract the load independent hardness from the experimental measurements. The energy balance model could not be successfully applied to the nanoindentation data. This is attributed in part to blunting of the nanoindenter tip, which resulted in changes in indenter contact area.

Mechanical response of thin films with helical microstructures

A nanoindentation technique has been applied to demonstrate the mechanical actuation of thin films fabricated by glancing angle deposition. The films were comprised of a porous layer whose microstructures consisted of helical columns that resembled springs. Surmounting the porous layer was a dense capping layer which served to redistribute the force of the nanoindenter tip and prevent it from penetrating the microstructured film. Atomic force microscope images and force versus displacement curves confirmed that there was an elastic regime to the displacements in the films when low forces were applied. The loading behavior of the porous films was compared with that of dense, unstructured films and revealed a marked difference between the two. A study of the measurements and results enabled such properties as the spring constant and resonant frequencies to be estimated, establishing a basis for future developments and applications in wave-type devices or resonators constructed from these microstructured thin films.

Chemically and geometrically enhanced focused ion beam micromachining

Improvements in focused ion beam (FIB) material removal rates utilizing geometric and chemical enhancement were investigated. Geometrical optimization of FIB micromachining of Permalloy and diamond was investigated to determine the magnitude of material removal rate gains that could be attained by increasing the angle of the ion beam with respect to the sample surface normal. The combination of geometrical optimization with chemical enhancement (C2Cl4 for Permalloy and H2O and XeF2 for diamond) was then investigated to determine whether additional gains in material removal rate could be attained. FIB sharpening of a diamond nanoindenter tip is also presented as a practical example of diamond micromachining with H2O as the removal rate enhancing species.