Preparation and mechanical properties of ultrafine grained metals

Ultrafine-grained polycrystalline metallic components (Cu, Au, Fe) have been prepared by means of the inert gas evaporation technique combined with an integrated uniaxial cold compaction device. The average grain sizes ranged typically from 20 nm to about 100 nm. The microstructure and impurity content of the as-pressed samples have been investigated by means of TEM and AES, respectively. The yield strength of ultrafine (30 nm) grained Cu specimens obtained in tensile tests compares well with respective values for heavily cold- worked coarse grained copper. Al slight heat treatment (150 degreeC/30 min.) improves the strain-to-fracture at slightly reduced yield strength values. The results are discussed within the picture of two concurrent processes determining the strength of ultrafine grained metals: Coble creep vs. grain boundary strengthening effect.