  Microcompression testing is used to probe the uniaxial stress-strain response
of a nanocrystalline alloy, with an emphasis on exploring how grain size and
grain boundary relaxation state impact the complete flow curve and failure
behavior. The yield strength, strain hardening, strain-to-failure, and failure
mode of nanocrystalline Ni-W films with mean grain sizes of 5, 15, and 90 nm
are studied using taper-free micropillars that are large enough to avoid
extrinsic size effects. Strengthening is observed with grain refinement, but
catastrophic failure through strain localization is found as well. Shear
banding is found to cause failure, resembling the deformation of metallic
glasses. Finally, we study the influence of grain boundary state by employing
heat treatments that relax nonequilibrium boundary structure but leave grain
size unchanged. A pronounced strengthening effect and increased strain
localization is observed after relaxation in the finer grained samples.
