Phase Transformations and Formation of Ultra-Fine Microstructure During Hydrogen Sintering and Phase Transformation (HSPT) Processing of Ti-6Al-4V

Research output: Journal Publications and ReviewsRGC 21 - Publication in refereed journalpeer-review

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Author(s)

  • Pei Sun
  • Zhigang Zak Fang
  • Mark Koopman
  • Yang Xia
  • James Paramore
  • K. S. Ravi Chandran
  • Jun Lu

Detail(s)

Original languageEnglish
Pages (from-to)5546-5560
Journal / PublicationMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume46
Issue number12
Publication statusPublished - 8 Sept 2015
Externally publishedYes

Abstract

The hydrogen sintering and phase transformation (HSPT) process is a novel powder metallurgy method for producing Ti alloys, particularly the Ti-6Al-4V alloy, with ultra-fine microstructure in the as-sintered state. The ultra-fine microstructure is obtained as a direct result of the use of H2 gas during sintering. The refinement of the microstructure during HSPT is similar to that of thermal hydrogen processing (THP) of bulk Ti alloys. For both THP and HSPT of Ti-6Al-4V alloy, the mechanisms of the grain refinement depend on the phase equilibria and phase transformations in the presence of hydrogen, which are surprisingly still not well established to date and are still subjected to research and debate. In recent work by the present authors, a pseudo-binary phase diagram of (Ti-6Al-4V)-H has been determined by using in situ synchrotron XRD and TGA/DSC techniques. Aided by this phase diagram, the current paper focuses on the series of phase transformations during sintering and cooling of Ti-6Al-4V in a hydrogen atmosphere and the mechanisms for the formation of the ultra-fine microstructures obtained. Using experimental techniques, including in situ synchrotron XRD, SEM, EBSD, and TEM, the microstructural refinement was found to be the result of (1) the precipitation of ultra-fine α/α2 within coarse β grains during an isothermal hold at intermediate temperatures, and (2) the eutectoid transformation of β → α + δ at approximately 473 K (200 °C).

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Citation Format(s)

Phase Transformations and Formation of Ultra-Fine Microstructure During Hydrogen Sintering and Phase Transformation (HSPT) Processing of Ti-6Al-4V. / Sun, Pei; Fang, Zhigang Zak; Koopman, Mark et al.
In: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, Vol. 46, No. 12, 08.09.2015, p. 5546-5560.

Research output: Journal Publications and ReviewsRGC 21 - Publication in refereed journalpeer-review