OR1-8
ISS-ELF

Ti-6Al-4VPrecision analysis of crystal growth rate of Ti-6Al-4V
using the onboard high-speed camera of the ISS-ELF
1,1,1,1,1,2,2,2,,2,3,3,3,4,1
1
1
1
1
Yuta KUSHIYA , Yuto UEDA , Koei KADOI , Haruka UENO , Yuji MABUCHI1, Chihiro HANADA1,Ryosei SAGUCHI2, Motoko YAMADA2, Hisashi SATO2, Yoshimi WATANABE2, Chihiro KOYAMA3,Hirohisa ODA3, Takehiko ISHIKAWA3, Yuki WATANABE4, and Shinsuke SUZUKI111234Waseda University,Nagoya Institute of Technology (NITech),Japan Aerospace Exploration Agency (JAXA),
Advanced Engineering Services (AES)

1. Introduction
Understanding the crystal growth of metal plays an important role in simulating materials processes, suchas casting or additive manufacturing. However, the crystal growth process is hard to observe because it iscovered by the crucible. In addition, the process is too fast to observe. Therefore, the levitation techniques withhigh-speed cameras are effective because those are containerless process and high in the time resolution.
By using the electrostatic levitation furnaces on the ground (ESL) and in the ISS (ISS-ELF), the methods toobtain the recalescence time1) and the crystal growth rate2) using the high-speed camera are established in theprevious studies, respectively. However, certain errors originated from the methodologies have not been
discussed well. Therefore, the aim of this study was to evaluate those errors quantitatively.
2. Experimental and analytical procedures
The samples were produced for Hetero-3D mission. Ti-6Al-4V powder was uniformly mixed with 2 mass%
TiC particles. Then, the mixed powder was sintered into a bulk. Subsequently, the bulk was cut and sphered.
The sample weighing around 25 mg was levitated to stabilize. The sample was levitated, melted, and solidified
in the ISS-ELF under the Ar atmosphere. The high-speed camera was employed to capture the solidification
process during recalescence with a resolution of 240 x 224 and a frame rate, f, of 10000 frames per second.
The crystal growth rate, v, was calculated by the captured images under the assumption that the sample wasa sphere because the molten droplet is sphered by the surface tension. The crystal growth rate was calculated
for every vertex of the solid phase in every frame and summarized in the time2).
3. Results
The representative series of recalescence images captured by the high-speed camera is shown in Fig. 1.
Nine images were obtained during recalescence. The brighter and darker region of the sample were identified
as a solid and liquid phase, respectively, because the solid phase illuminate during the recalescence. A squaresolid phase grew on the spherical surface of the sample. The brightness and contrast were adjusted to clarify
the solid-liquid interface. The crystal growth rate is also shown in Fig. 1.
1 of 2

Figure 1. Representative series of images obtained by the high-speed camera and crystal growth rate witherror. Only the upper vertexes indicated by red circles are shown as representatives.

4. Discussion
The error was categorized into three factors. The rotation of the sample during the levitation is the first,
which comes from the movement of the sample. The error was calculated from the rotating interval and it wasless than 0.03% compared to the obtained crystal growth rate at every vertex of every timestep. The distortionof the high-speed camera is originated from the equipment, which is the unique value of the geometry
depending on the installed lens. The value is 0.18%. The quantification error is the last, which is generated
when the visible light is converted into the digits at the sensor array of the high-speed camera. The errors wereless than 10%. The schematic illustration is shown in Fig. 2. Those errors are summed and indicated in Fig. 1.
The error is smaller than the change in the crystal growth rate because the error bars were not overwrapped
between 0.15 ms and 0.25 ms, or 0.45 ms and 0.65 ms. Therefore, the solidification rate can be said to have thetendency to decelerate first and then to accelerate.

Figure 2. Schematic illustration of three factors of error.

5. Conclusions
The error was summarized in the three factors; rotation of the sample of 0.03%, distortion of the highspeed camera of 0.18%, and quantification error of up to 10% compared to the calculated crystal growth rate.
Although every factor originating from the levitation method or experimental setup was quantitatively
evaluated, the amount was smaller enough to recognize that the crystal growth rate of this sample inHetero-3D first decelerated and then accelerated.
References
1)

2)

Y. Mabuchi, C. Hanada, Y. Ueda, K. Kadoi, H. Aoki, R. Saguchi, M. Yamada, H. Sato, Y. Watanabe, S. Ozawa, S.
Shiratori, S. Nakano, C. Koyama, H. Oda, T. Ishikawa, Y. Watanabe, and S. Suzuki: Analysis Method for RecalescenceTime Obtained Using High-Speed Camera for Solidification Experiments at the Electrostatic Levitation Furnace inthe International Space Station. Int. J. Microgravity Sci. Appl., 41 (2024) 410101, DOI: 10.15011/jasma.41.410101.
Y. Kushiya, Y. Mabuchi, C. Hanada, Y. Ueda, K. Kadoi, H. Aoki, R. Saguchi, M. Yamada, H. Sato, Y. Watanabe, C.
Koyama, H. Oda, T. Ishikawa, Y. Watanabe, and S. Suzuki: Abstract of JASMAC-35 (2023) P24.
© 2024 by the authors. Submitted for possible open access publication under
the terms and conditions of the Creative Commons Attribution (CC BY) license(http://creativecommons.org/li censes/by/4.0/).

2 of 2