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Formation of nanocrystalline β structure in metastable beta Ti alloy during high pressure torsion: the role played by stress induced martensitic transformation
journal contributionposted on 2015-09-15, 00:00 authored by A Zafari, X S Wei, Wei XuWei Xu, K Xia
High pressure torsion was conducted to obtain nano-sized β grains in a metastable Ti-5553 alloy. Much finer grains of <50 nm were achieved, compared to >100 nm in a stable Ti-20 wt.% Mo alloy. The more effective grain refinement was attributed to stress induced martensitic transformation in the former, leading to the formation of thin α" plates which divide β grains into smaller domains. Further deformation resulted in a reverse α" to β transformation with decreasing α" sizes, generating a completely nano β grain structure at very large straining. A detailed description of the β grain refinement mechanism is provided. The reverse transformation is shown to be caused by the significantly increased free energy below a critical α" size of ∼10 nm, consistent with experimental observations. It is also calculated that extremely high energies were required for the formation of α" in nano-sized β grains, making further martensitic transformation impossible. It is concluded that the stress induced martensitic transformation and the subsequent reverse transformation are critical to producing nano-grained metastable β Ti alloys.
Pagination146 - 155
LocationAmsterdam, The Netherlands
Publication classificationC Journal article; C1.1 Refereed article in a scholarly journal
Copyright notice2015, Acta Materialia Inc.
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β titanium alloysSevere plastic deformation (SPD)High-pressure torsionMartensitic phase transformationGrain refinementScience & TechnologyTechnologyMaterials Science, MultidisciplinaryMetallurgy & Metallurgical EngineeringMaterials Sciencebeta titanium alloysSEVERE PLASTIC-DEFORMATIONTITANIUM-ALLOYGRAIN-SIZEREFINEMENTTENSILEBEHAVIORMICROSTRUCTURESTABILITYMETALS