No abstract

A new method for evaluating modulus and hardness from nanoindentation load/ displacement curves is presented. As a spherical indenter penetrates an elastoplastic half-space, the elastic displacement above the contact line is presumed to diminish in proportion to the total elastic displacement under the indenter. Applying boundary conditions on the elastic and plastic displacements for elastic and rigid plastic contacts leads to an expression that can be best fit to the entire unloading curve to determine E ‫ء‬ , the reduced modulus. Justification of the formulation is presented, followed by the results of a preliminary survey conducted on three predominantly isotropic materials: fused quartz, polycrystalline Al, and single crystal W. Diamond tips with radii ranging from 130 nm to 5 mm were used in combination with three different nanoindentation devices. Results indicate that the method gives property values consistent with accepted values for modulus and hardness. The importance of surface roughness and indentation depth are also considered.

A simple superposition solution for a point-loaded elastic plate on a soft substrate is proposed. The solution considers a "drumhead" being elastically bent into a compliant substrate that is viscoelastic-plastic. With simplifying assumptions it is found that the drumhead and substrate support loads proportional to d 1/2 and d 3/2 , respectively, where d is the vertical point displacement. At fixed displacement, relaxation proceeds at high loads, but if sufficiently unloaded, recovery or increased load results with time. Qualitative verification of the time-dependent drumhead solution is shown by relaxation and recovery data on polycarbonate covered by polysiloxane, composite or diamondlike carbon (DLC) coatings, and films.

In this study we combined nanoscratch testing with a multilayer sapphire and aluminum nitride single-substrate system to determine the effects of interface composition and structure on susceptibility to fracture of hard, thin tantalum nitride films. Nanoindentation tests showed that the elastic moduli of the tantalum nitride and aluminum nitride films, as well as the sapphire substrate, were essentially equal at 400 GPa. On both portions of the substrate, these tests also showed that near surface hardness was near 35 GPa. Nanoscratch tests triggered long blisters and circular spalls on both the sapphire and aluminum nitride portions of the substrate. The blisters showed that the tantalum nitride film was subjected to a compressive residual stress of 26.7 GPa. The spalls showed that failure occurred along the tantalum nitride film-substrate interface regardless of substrate composition. Most importantly, the blisters and spalls showed that the mode I component of the fracture energies was essentially equal on both substrate materials at a value near 3.1 J͞m 2 . These energies are on the order of the energies for metallic bonding.

In this study, we employed nanoindentation testing to determine load rate and load rate change effects on the plastic response of a single crystal aluminum sample and of an 80 nm thick vapor deposited aluminum film on a sapphire substrate. The load rate tests showed that the thin film plastic properties exhibited a much stronger dependence on loading rate than the properties of the aluminum single crystal. In contrast, the load rate change data indicated a weak dependence of thin film plastic properties on loading. Scanning probe microscopy showed that the difference in behavior can be attributed primarily to pileup effects on contact area which increased with contact depth and loading rate. When contact area was corrected for increased pileup height, plastic properties were reduced to single crystal aluminum values.