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The deformation and failure of commercial-purity (CP) titanium (grade 2) and AISI 4340 steel (tempered to R c 35) during equal channel angular extrusion were determined at temperatures between 25 ЊC and 325 ЊC and effective strain rates between 0.002 and 2.0 s Ϫ1 . The CP titanium alloy underwent segmented failure under all conditions except at low strain rates and high temperatures. By contrast, the 4340 steel deformed uniformly except at the highest temperature and strain rate, at which it also exhibited segmented failure. Using flow curves and fracture data from uniaxial compression and tension tests, workability analysis was conducted to establish that the failures were a result of flow localization prior to the onset of fracture. This conclusion was confirmed by metallographic examination of the failed extrusion specimens.

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Deformation during conventional (nonisothermal) hot working of metals via equal-channel angular extrusion (ECAE)was investigated using two-dimensional (2-D) and three-dimensional (3-D) finiteelement modeling (FEM) analysis. The effects of material flow properties, die-workpiece heat-transfer and friction conditions, and die design on metal flow were examined. Friction and die design were shown to be the most important parameters governing the formation of dead-metal zones during extrusion. On the other hand, thermal gradients induced by die chill and deformation heating were found to exacerbate the extent of flow localization that arises due to material-flow softening alone. The FEM predictions were validated by ECAE experiments on a Ti-6Al-4V alloy with a colony alpha microstructure. Preforms exhibited minor edge cracking and mild flow localization during extrusion at 985 ЊC, but severe shear localization and fracture during extrusion at 900 ЊC. The 2-D FEM simulations predicted deformation detail, including shear localization, that was in good agreement with the experimental results, but 3-D FEM simulations were required to realistically predict die chill. A combined approach, in which thermal data were extracted from 3-D simulations and inserted into 2-D simulations, produced load-stroke and fracture predictions in general agreement with measured values.

The deformation behavior of Ti-6Al-4V during high-temperature equal channel angular extrusion (ECAE) with or without an initial increment of upset deformation was determined for billets with either a lamellar or an equiaxed alpha preform microstructure. For conventional ECAE (i.e., deformation by simple shear alone), flow localization and fracture occurred at temperatures between 900 ЊC and 985 ЊC. In contrast, billets deformed at temperatures between 845 ЊC and 985 ЊC using an initial increment of upset deformation immediately followed by the simple shear deformation of ECAE exhibited uniform flow with no significant cracking or fracture. A simple flow-localization criterion was used to explain the influence of preupsetting on the suppression of localization in billets with the lamellar microstructure. The suppression of flow localization for the equiaxed microstructure and the elimination of edge cracking for both types of microstructures were explained in terms of heat transfer (die chill) and workpiece geometry. Further evidence of the relative importance of microstructural and thermal effects was extracted from the results of two-pass extrusions, the first with upsetting and the second without upsetting.