Using heat treatments, high-pressure torsion and post-deformation annealing to optimize the properties of Ti-6Al-4V alloys

Experiments were conducted to investigate the processing parameters that may be used to optimize the properties of Ti-6Al-4V alloys. The alloy was initially subjected to two different heat treatments leading to the formation of martensitic α′ and lamellar α+β microstructures and then both materials were processed by high-pressure torsion (HPT) for 10 turns at room temperature. This gave significant grain refinement to the nanometer range in both conditions and the occurrence of an allotropic hcp to fcc phase transformation in the martensitic alloy. These nanostructured alloys were subjected to post-deformation annealing (PDA) at temperatures in the range of 473-1023 K. The results show the hardness increases slightly to 773 K due to α′+fcc→α+β+fcc and α→α+β phase transformations in the martensitic α′ and lamellar α+β alloys and then decreases up to 1023 K due to recrystallization and grain growth. An optimum property of a very high yield strength (∼1120 MPa) and ultimate tensile strength (∼1200 MPa), together with excellent ductility (elongation to failure of ∼26%), was achieved in the Ti-6Al-4V martensitic alloy processed by a combination of HPT followed by PDA at 873 K for 60 min.

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