Grain refinement and superplastic flow in a fully lamellar Ti-6Al-4V alloy processed by high-pressure torsion

Abstract

A cold-rolled Ti-6Al-4V alloy was subjected to consecutive heat treatments at 1283 K for 1 h and at 823 K for 3 h in order to produce a fully lamellar microstructure. Thereafter, the material was processed by high-pressure torsion (HPT) through various numbers of turns up to a maximum of 30. It is shown that the HPT processing leads to exceptional grain refinement with average grain sizes of ~70 and ~50 nm after 20 and 30 turns, respectively. Tensile testing was conducted at 873 and 923 K with different initial strain rates using the material processed through 20 turns of HPT and this gave a maximum superplastic elongation of 820% at the relatively low temperature of 923 K when testing with an initial strain rate of 5.0 × 10−4 s−1. The associated strain rate sensitivity for this low temperature superplasticity was estimated as m ≈ 0.5 which is consistent with flow by grain boundary sliding.

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Identifiers

ORCID for Yi Huang: orcid.org/0000-0001-9259-8123

ORCID for Terence G. Langdon: orcid.org/0000-0003-3541-9250

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