The effect of cooling conditions on Ti 6%Al 4%V microstructure observed using high-temperature in-situ scanning electron microscopy

Abstract

This study focuses on continuous imaging of microstructural changes in Ti 6% Al 4% V when cooling from the β transus of ~ 995 °C or above. A range of microstructures were obtained by accessing different cooling rates. With cooling rates of 0.1–0.5 °C/s, lamellar microstructures were observed, which initiate in a colony microstructure below temperatures of ~ 930 °C. When the lamellar microstructure began forming at grain boundaries, cooling was interrupted to further observe the kinetics in the system. Lamellae changed in projected length from 40 µm to ~ 160–320 µm over three minutes at ~ 930 °C, within the α + β mixed phase. On further time at temperature, the lengthening of lamellae stagnated. With further cooling at 0.1 °C/s, lamellae grew in projected width, while the projected length remained the same. In addition, a surface topography formed at elevated temperatures (around 800 °C), evolved during the α to β heating transition, and persisted upon cooling.

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Acknowledgments

We acknowledge the sponsorship of the National Science Foundation, through CMMI-1647005 (equipment design and construction) and CMMI-1729336 (in-situ experimentation in Ti 6-4) awards for funding this work, as well as the use of characterization and cleanroom facilities within the Center for Materials, Devices and Integrated Systems at Rensselaer Polytechnic Institute. We acknowledge Brent Engler for useful discussions on lamellar growth. In addition, we acknowledge Konrad Weiss, Farhad Ghaleh, and George Lanzarotta from Kammrath and Weiss GmbH., for their expertise and assistance with equipment development.

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Correspondence to Robert Hull.

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Kane, G.A., Andersen, D., Frey, M.D. et al. The effect of cooling conditions on Ti 6%Al 4%V microstructure observed using high-temperature in-situ scanning electron microscopy. Journal of Materials Research (2021). https://doi.org/10.1557/s43578-020-00102-4

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Keywords

  • Microstructural evolution
  • Surface faceting
  • Phase change kinetics
  • Lamellar growth
  • Scanning electron microscopy