Achieving grain refinement and enhanced mechanical properties in Ti–6Al–4V alloy produced by multidirectional isothermal forging

This study investigated the principle of multidirectional isothermal forging (MDIF) and determined the major microstructural evolution features and unique room-temperature mechanical properties of extra-low interstitial-grade Ti–6Al–4V alloy. The grain refinement mechanism, grain boundary characteri...

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Bibliographic Details
Published in:Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2017-04, Vol.692, p.127-138
Main Authors: Zhang, Z.X., Qu, S.J., Feng, A.H., Shen, J.
Format: Article
Language:English
Subjects:
Dislocations
Dynamic recrystallization
Forging
Grain boundaries
Grain refinement
Grain size
Mechanical properties
Mechanical property
Microstructure
Multidirectional isothermal forging
Phase transitions
Recrystallization
Substructures
Tensile strength
Titanium base alloys
Ti–6Al–4V
Ultimate tensile strength
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Summary:This study investigated the principle of multidirectional isothermal forging (MDIF) and determined the major microstructural evolution features and unique room-temperature mechanical properties of extra-low interstitial-grade Ti–6Al–4V alloy. The grain refinement mechanism, grain boundary characteristics, and phase transformation during MDIF were explored. After three-step MDIF, a homogeneous microstructure with a grain size of about 0.5µm was produced. The ultrafine grained Ti–6Al–4V alloy exhibited high yield strength (1170MPa), high ultimate tensile strength (1190MPa), and good ductility (10.4%). The mechanism of grain refinement during MDIF included continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). Grain subdivision resulted from CDRX or the transformation of cellular dislocation substructures into new ultrafine grains. The necklace of new DDRX grains formed along the initial grain boundaries of the Ti–6Al–4V alloy. The main strengthening mechanisms were grain boundary and dislocation strengthening. The strength and grain size followed the typical Hall–Petch relationship.
ISSN:0921-5093
1873-4936
DOI:10.1016/j.msea.2017.03.024