The effect of hydrogenation on the ECAP compaction of Ti-6Al-4V powder and the mechanical properties of compacts

The effect of hydrogen content on the compaction of Ti-6Al-4V powder at low temperatures, namely 500 degrees C, using equal channel angular pressing (ECAP) with back pressure has been investigated. The properties of the compacts before and after a heat treatment and de-hydrogenation cycle have been determined. Compaction of powder by ECAP (500 degrees C and 260 MPa) has shown maximum levels of relative density of 99.3% and 99.4% when charged with 0.05-0.1 wt.% and 0.61-0.85 wt.% of hydrogen, respectively. After the de-hydrogenation heat treatment the diffusion bonding between individual powder particles was completed and the microstructure was altered, depending on the level of hydrogen content. Two local maxima of 99.2% and 98.1% were observed in the measured density of consolidated compacts for hydrogen contents between 0.05 wt.% and 0.1 wt.% and between 0.61 wt.% and 0.85 wt.%, respectively. However, the mechanical properties of the compacts within these two ranges of hydrogen content were significantly different due to a difference in the observed microstructure. An exceptionally high ductility of 29%, in combination with a relatively high strength of similar to 560 MPa, was measured in a shear punch test on specimens which had a prior hydrogen level of 0.05 wt.% before the heat treatment. It was shown that material consolidated from powder hydrogenated to low levels of hydrogen before compaction has the potential to offer substantial improvements in mechanical properties after a suitable heat treatment. (C) 2009 Elsevier B.V. All rights reserved.