Processing and Fabrication of Advanced Materials VI PDF

Abstract

There is considerable current interest in the fabrication of polycrystalline metals with ultrafine grain sizes, typically with grain sizes of the order of -100 nm. Several techniques are in use to prepare these materials but generally it is very difficult to fabricate large bulk samples and invariably the samples contain some residual porosity. This paper describes an alternative procedure in which an ultrafine grain size is introduced into a bulk material by intense plastic straining. There are two standard procedures which are used to produce the high strain: torsion straining under a high pressure and equal-channel angular (ECA) pressing. The latter procedure involves pressing a material repetitively through a special die in which two channels of equal cross-section intersect at a high angle. In the present work, experiments were conducted to investigate the development of an ultrafine microstructure in samples of pure Al using the ECA pressing technique. The results show that large fully-dense samples may be produced using this processing method with grain sizes of the order of - 1 IJ.m. However, the precise microstructural characteristics depend upon the number of separate pressings through the die and whether or not the sample is rotated between each pressing.

Edited by: K.A.Khor, T.S.Srivatsan, J.J. Moore