Ultrafine grained metals and metal matrix nanocomposites fabricated by powder processing and thermomechanical powder consolidation

Ultrafine grained metals and metal matrix nanocomposites with enhanced strength and good tensile ductility for structural applications have been successfully fabricated by processing and thermomechanically consolidating powders and, in some cases, post-consolidation heat and thermomechanical treatments. This paper provides an overview of the substantial amount of research work mainly published by the author?s research groups rather than a comprehensive review of the vast amount of very active research work published in this area. The microstructures and tensile properties of the samples fabricated and the correlations between them strongly suggest that the synergistic effects of grain boundary strengthening and intragranular ceramic (and other hard) nanoparticles are highly desirable for significantly enhancing the tensile yield strength and maintaining generally good tensile ductility. The extra boundaries between hard regions and soft regions introduced by heterogeneous microstructure can further enhance the strength of the material without sacrificing tensile ductility by inducing back stress in the soft regions. However, these boundaries also induce forward stress in the hard regions which has a weakening effect on them and needs to be managed by dispersing nanoparticles in the hard regions or other means.