COMPRESSIVE MECHANICAL-BEHAVIOR OF NANOCRYSTALLINE FE INVESTIGATED WITH AN AUTOMATED BALL INDENTATION TECHNIQUE

Nanocrystalline (nc) iron was produced by mechanical attrition and com pacted into near fully dense samples. Isothermal annealing at 800 K re sulted in grain sizes between 15 and 24 nm. A newly available Automate d Ball Indentation system was used to study the compressive mechanical properties of the samples. The ABI method proved useful in examining the mechanical properties of ne iron on a more quantitative level than previously possible by conventional hardness testing methods. Stress- strain curves were obtained which indicated a compressive behavior sim ilar to that of perfectly plastic materials: low strain hardening at h igh flow stresses around 3 GPa and a low room-temperature strain-rate sensitivity. The flow stresses were independent of the grain size in t he range of the present study. The deformation pile-up around the inde ntations seems to have formed inhomogeneously, exhibiting intense plas tic deformation in localized shear bands. (C) 1998 Elsevier Science S. A. All rights reserved.