Test rate effects on the mechanical behavior of thin aluminum films

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.