Work hardening of quaternary powder metallurgy Ti alloys

Abstract

The concurrent addition of Al as α stabiliser and Nb and Cu or Mn as β stabilisers was used to design new powder metallurgy quaternary Ti alloys and investigate their manufacturability and consequent performance. It is found that the powder blend's compressibility decreases with the total amount of alloying elements due to the characteristics of the powders used. Consequently, the sintered density of the quaternary Ti alloys decreases and slightly higher values are achieved if Mn instead of Cu is used, despite the higher diffusivity of Cu at the sintering temperature. The quaternary Ti alloys are characterised by a lamellar microstructure comprising α grain boundaries and α+β lamellae where the amount and type of alloying elements determine the coarseness of the microstructural features. This results in stronger and harder but less ductile quaternary Ti alloys for higher alloying elements contents and for stronger β stabilisers, although of their overall elastoplastic behaviour. Because of their lamellar microstructure, the quaternary Ti alloys show similar deformation behaviour but the actual work hardening rate is governed by the fineness of the microstructure.