Impurity scavenging, microstructural refinement and mechanical properties of powder metallurgy titanium and titanium alloys by a small addition of cerium silicide

A small addition (≤0.5 wt%) of cerium silicide (CeSi2) to powder metallurgy (PM) commercially pure Ti (CP-Ti), Ti-6Al-4V and Ti-10V-2Fe-3Al (all in wt%) results in substantial microstructural refinement and noticeably improved ductility with marginally improved sintered density. CeSi2 is unstable and decomposes between 1423 K and 1473 K. The Si goes into solid solution in β-Ti and is responsible for the improved sintered density while the Ce scavenges both oxygen (O) and chlorine (Cl) from the Ti powder and therefore improves tensile ductility. The resulting CeO2 and CeClxOy particles generally exist along or close to the prior-β grain boundaries. The substantial microstructural refinement in terms of both the prior-β grain size and the subsequent α-Ti lath size is attributed to the grain boundary pinning effect of the CeO2 particles. The optimum concentration of CeSi2 is approximately 0.5 wt%, beyond which both the sintered density and tensile elongation drop with increasing addition of CeSi2. CeSi2 can be a practical form of Ce addition to PM Ti alloys for impurity scavenging, microstructural refinement and tensile ductility improvement.