Correlation between microstructure and tensile properties of powder metallurgy Ti-6Nb-x(Fe or Mn) alloys

The individual addition of Nb, Fe, or Mn to Ti has been greatly studied, but their combined addition has been much less understood, especially for the Ti-Nb-Mn system. Moreover, the full potential of using powder metallurgy to reduce their manufacturing cost has not been properly exploited and, even though proposed for structural applications, rarely tensile properties were reported. In this study new powder metallurgy Ti-6Nb-x(Fe or Mn) alloys were produced and the correlation between their microstructure and tensile properties established. It was found that, for a similar addition of Nb, Mn is a stronger eutectoid beta stabiliser compared to Fe leading to more refined lamellar structures and a greater amount of stabilised beta phase. Accordingly, higher tensile properties (832-1050 MPa yield stress and 910-1080 MPa ultimate tensile strength) and lower ductility (6.3-1.7 %) were, thus, obtained in ternary Ti-Nb-Mn alloys compared to Ti-Nb-Fe alloys, but the actual stress/strain pairs and hardness are the compromise between the volumetric fraction of residual porosity (3.6-4.9 %), which increases with the amount of alloying elements, and the microstructural changes induced by actual chemical composition.(c) 2022 Elsevier B.V. All rights reserved.