Low-temperature compaction of Ti-6Al-4V powder using equal channel angular extrusion with back pressure

Equal channel angular extrusion (ECAE), with simultaneous application of back pressure, has been applied to the consolidation of 10mm. diameter billets of pre-alloyed, hydride-dehydride Ti-6Al-4V powder at temperatures < 400 degrees C. The upper limit to processing temperature was chosen to minimise the potential for contamination with gaseous constituents potentially harmful to properties of consolidated product. It has been demonstrated that the application of ECAE with imposed hydrostatic pressure permits consolidation to in excess of 96% relative density at temperatures in the range 100-400 degrees C, and in excess of 98% at 400 degrees C with applied back pressure >= 175 MPa. ECAE compaction at 20 degrees C (back pressure= 262 MPa) produced billet with 95.6% relative density, but minimal green strength. At an extrusion temperature of 400 degrees C, the relative density increased to 98.3%, for similar processing conditions, and the green strength increased to a maximum 750MPa. The relative density of compacts produced at 400 degrees C increased from 96.8 to 98.6% with increase in applied back pressure from 20 to 480 MPa, while Vickers hardness increased from 360 to 412 HV. The key to the effective low-temperature compaction achieved is the severe shear deformation experienced during ECAE, combined with the superimposed hydrostatic pressure. (c) 2008 Elsevier B.V. All rights reserved.