MECHANICAL-PROPERTIES, DUCTILITY, AND GRAIN-SIZE OF NANOCRYSTALLINE IRON PRODUCED BY MECHANICAL ATTRITION

The main goal of this investigation is to determine the influence of g rain size on the mechanical properties and, specifically, the intrinsi c ductility of nanocrystalline (nc) Fe. Ball-milled nc Fe was consolid ated into compacts of near theoretical density by uniaxial warm pressi ng. Compaction parameters and annealing treatments resulted in a range of grain sizes for subsequent mechanical testing. The miniaturized di sk bend test, hardness, and the automated ball indentation (ABI) metho d were used to test nanocrystal (nc) iron in compression and tension. The deformation and fracture morphologies of the tested samples were c haracterized by light and scanning electron microscopy. The hardness, as a function of the grain size, was described with a Hall-Fetch slope , which was smaller than that in coarse-grained Fe. In tension, the ma terial failed in a macroscopically brittle manner, while local ductili ty in very concentrated shear bands was observed. The compressive char acteristics of the nc Fe were similar to those of a perfectly plastic material. The results are discussed in the context of the mechanical b ehavior of coarse-grained polycrystalline metals and alloys.