Microstructural characterisation of Ti-Nb-(Fe-Cr) alloys obtained by powder metallurgy

摘要

beta alloys based on the Ti-Nb alloy system are of growing interest to the biomaterial community. The addition of small amounts of Fe and Cr further increases beta-phase stability, improving the properties of Ti-Nb alloy. However, PM materials sintered from elemental powders are inhomogeneous due to restricted solid state diffusion and mechanical alloying provides a route to enhance mixing and elemental diffusion. The microstructural characteristics and bend strength of Ti-Nb-(Fe-Cr) alloys obtained from elemental powder mixture and mechanical alloyed powders are compared. Mechanical alloying gives more homogeneous compositions and particle morphology, characterised by rounded, significantly enlarged particles. In the sintered samples a and b phase are observed. The a phase appears at the grain boundaries and in lamellae growing inward from the edge, and is depleted in Nb. The beta phase is enriched with Nb, Fe and Cr. The addition of Fe and Cr significantly increases the mechanical properties of Ti-Nb alloys, providing increased ductility.