Enabling the development of ductile powder metallurgy titanium alloys by a unique scavenger of oxygen and chlorine

Abstract

NdB6 can effectively react with the surface titanium oxide films to form an initial NdBO3 layer at about 670 °C, just prior to their dissolution. Two thirds of all the oxygen scavenged during sintering occurred in the α-Ti phase region through this reaction. NdBO3 layer continues to grow by diffusion of oxygen until 1130 °C, beyond which NdBO3 decomposes into Nd2O3 dispersoids and Nd2O3 further reacts with chlorine to form NdClxOy. The unique oxygen-scavenging process prior to the active dissolution of oxide film makes NdB6 more effective in scavenging oxygen than other rare earth hydrides, resulting in better tensile elongation. The addition of NdB6 also leads to the improved sintered density, substantial microstructural refinement and dispersion strengthening by Nd-containing compounds and TiB. The optimal addition level of NdB6 is 0.3 wt.%, beyond which large Nd2O3 aggregates and an increased number of TiB whiskers were formed. This is detrimental to the ductility.