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

  • : Angélica Amigó 1, Jenny Cecilia Zambrano1, Saul Martinez1, Vicente Amigó1
  • : 1Universidad Politécnica de Valencia
  • : PDF Download
  • : 2014

Abstract

Ti β-alloys exhibit interest in implant biomaterial because of its biocompatible nature and low elastic modulus when compared with other materials such as stainless steel or CoCr. An approximation to the value of elastic modulus of cortical bone is achieved, minimizing the problems of stress shielding and bone resorption. The addition of small amounts of Fe and Cr increases β phase stability, improving the properties of the Ti-Nb alloy. These elements have a eutectoid transformation that reduce β → α temperature transformation, and produce two-phase structure at room temperature. The use of powder metallurgy can get parts with different geometries, high quality and decreasing the production costs. However, it has the problem of lack of solid state diffusion of these metals. This is why, to improve mixing and diffusion of the elements mechanical alloying of elemental powders is used. This paper studies the microstructural characterization and correlation with the mechanical properties obtained by bending tests of Ti-Nb-(Fe-Cr) alloys obtained by conventional powder metallurgy with elemental powder mixture and mechanical alloying, studying morphology, homogeneity and microstructure. Subsequently compacted and sintered samples (2h 1280°C under high vacuum) and the microstructural characterization and mechanical properties of compacts obtained with both materials are compared. The mechanical alloying allows a much more homogeneous composition and morphology mixture, appearing rounded larger particles. In the microstructural characterization of the sintered samples appear two phases, alpha and beta. The alpha phase appears in grain boundaries and in lamellae growing from the edge inward, formed mainly by Ti and lower niobium content than nominal. The beta phase is enriched with Nb, Fe and Cr. The addition of these elements increases considerably the mechanical properties of Ti-Nb alloys, providing increased ductility. Despite the β stabilizing effect of these elements keeps forming alpha phase in the grain boundaries decreasing the ductility and toughness expected.
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