Microstructure development during equal-channel angular pressing of titanium

The development of microstructure during equal-channel angular pressing (ECAP) of commercial-purity titanium was investigated to establish the mechanisms of grain refinement and strain accommodation. Samples were deformed at 623 K via three different processing routes: A, B, and C. After the first pass, transmission electron microscopy (TEM) revealed that the strain imposed by pressing was accommodated mainly by {10 (1) over bar1} deformation twinning. During the second pass, the deformation mechanism changed to dislocation slip on a system which depended on the specific route. For route C, prism (a) and pyramidal (c + a) slip occurred within alternating twin bands. For route B, prism a slip was the main deformation mechanism. For route A, deformation was controlled by basal a slip and micro-twinning in alternating twin bands. The variation in deformation behavior was interpreted in terms of the texture formed during the first pass and the Schmid factors for slip during subsequent deformation. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.