<Abstrate>

Considerable interest has centered recently on the processing of materials with

ultra-fine grain sizes, typically <100 nm. These materials may be prepared by various

techniques including gas condensation and subsequent in situ consolidation under

high vacuum, high energy ball milling and sliding wear. Alternatively, it has been

shown that submicrometer-grained structures may be produced in a wide range of

materials (e.g. pure metals, metallic alloys including superalloys, intermetallics,

semiconductors) by subjecting these materials to a very high plastic strain 

using either equalchannel angular (ECA) pressing  or torsion straining under

high pressure. These latter procedures usually give grain sizes in the

submicrometer range of ~100-200 nm although there are reports of grain sizes as

small as ~50 nm. In practice, ECA pressing is an especially attractive processing

method because it provides the capability of producing large bulk samples which are

free from any residual porosity.
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