Metallurgical and Materials Transactions A

, Volume 46, Issue 12, pp 5546–5560 | Cite as

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

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


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).


Dehydrogenation Grain Boundary Eutectoid Transformation Vacuum Sinter Blended Elemental 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



The authors acknowledge funding support by the U.S. Department of Energy, Innovative Manufacturing Initiative (DEEE0005761), through the Advanced Manufacturing Office and the Office of Energy Efficiency and Renewable Energy. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. The first author acknowledges the valuable assistance of Dr. Xiangyi Luo, Mr. Chun Yu, and Mr. Rick Spence for synchrotron X-ray experiments at Argonne National Lab, and the help of Dr. Paulo Perez and Dr. Matt Nowell for collecting EBSD data.


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Copyright information

© The Minerals, Metals & Materials Society and ASM International 2015

Authors and Affiliations

  • Pei Sun
    • 1
  • Zhigang Zak Fang
    • 1
  • Mark Koopman
    • 1
  • Yang Xia
    • 1
  • James Paramore
    • 1
  • K. S. Ravi Chandran
    • 1
  • Yang Ren
    • 2
  • Jun Lu
    • 3
  1. 1.Department of Metallurgical Engineeringthe University of UtahSalt Lake CityUSA
  2. 2.X-ray Science Division, Advanced Photon SourceArgonne National LaboratoryLemontUSA
  3. 3.Chemical Science and Engineering DivisionArgonne National LaboratoryLemontUSA

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