Fatigue-induced grain coarsening in nanocrystalline platinum films

Mechanisms to explain the unique mechanical behavior of nanograined metals focus primarily on grain and grain boundary mobility. In most nanograined metal materials systems (both pure and alloyed) it has not been possible to decouple these time- and cycle-dependent contributions. In contrast, the 460nm thick, (111) textured, nanograined platinum thin films evaluated in this work have robust grain morphologies that allow us to uniquely identify the fatigue damage accumulation processes. Unlike other reports of face-centered cubic metal behavior, the platinum films exhibited a particularly limited range of fatigue crack growth (<3MPa√m) with extremely large (∼10.5) power law exponents typically associated with fatigue of structural ceramics and ordered intermetallics. Transmission electron microscopy and fatigue crack growth data suggest that the crack growth mechanism appears to be intrinsic in origin and dislocation mediated.