Mechanical behavior of nanocrystalline metals

The influence of grain size or cell size on the mechanical behavior of metals is well known, although debate continues about details of defect control mechanisms. In the past, difficulty in producing bulk samples with grain sizes smaller than about 1 {mu}m limited mechanical behavior studies in finer-grained materials. Expressions relating strength to grain size, determined from studies of coarse-grained materials, suggest that reducing grain size into the sub-micrometer range results in increased mechanical strength at low homologous temperatures. At high temperatures, diffusional creep effects may lead to increased ductility. This paper reports the major results to date of an ongoing study of the mechanical behavior of nanocrystalline metals produced by the inert-gas condensation method; some results have been reported elsewhere. Studies of the tensile strength, low-temperature creep and Vickers microhardness of Cu, Pd and Ag reported here are complemented in this broader study by processing studies, x-ray grain-size and strain analyses, and high resolution microscopy studies of nanostructure and microstructure. The work provides a basis for predicting low-temperature mechanical behavior of ultrafine-grained metals, subject to some significant constraints imposed by the processing conditions. 16 refs., 2 figs., 3 tabs.