P24
Hetero-3D
Ti6Al4V

ISS-ELF

Elucidation of Crystal Growth Rate of Ti6Al4V Using theHigh-Speed Camera in the ISS-ELF in Hetero-3D
1,1,1,1,1,2,2,2,,2,3,3,3,4,1
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1Yuta KUSHIYA , Yuji MABUCHI , Chihiro HANADA , Yuto UEDA1, Koei KADOI1, Hirokazu AOKI1,Ryosei SAGUCHI2, Motoko YAMADA2, Hisashi SATO2, Yoshimi WATANABE2, Chihiro KOYAMA3,Hirohisa ODA3, Takehiko ISHIKAWA3, Yuki WATANABE4, and Shinsuke SUZUKI1112341.

Waseda University,Nagoya Institute of Technology,
Japan Aerospace Exploration Agency (JAXA),
Advanced Engineering Services (AES)

Introduction
In the space mission, Hetero-3D, a crystal growth process of a droplet of Ti6Al4V alloy was recorded using

the high-speed camera (HSC) in the electrostatic levitation furnace in the International Space Station (ISS-ELF).
Though it is known that crystals in undercooled liquid metal grow in rectangular shapes during recalescenceand tend to grow their corners1), the time variation of crystal growth rate is still uncertain. Thus, the objectiveof this study was to establish and verify the calculating method of the local crystal growth rate to discuss thekinetics of crystal growth during recalescence by analyzing the displacement of the solid-liquid interface (SLI).
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Experimental Procedures
Ti6Al4V powder was mixed with 2 mass% TiC particles, sintered by spark plasma sintering method, andcut into cubes of approximately 20 mg. After that, the cube was shaped into a sphere by arc melting. The
specimen was levitated, melted, and solidified in the ISS-ELF. The crystal growth process and the temperature
history during recalescence were recorded by the HSC at 10,000 fps and a pyrometer at 100 Hz, respectively.

Figure 1. Solidification images during recalescence captured using the high-speed camera.

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3.

Results
The crystal growth process resulted in 53 K of the degree of undercooling in 9 frames at 10,000 fps.

Representative frames of the specimen are shown in Fig. 1. It may be back side that the observed crystal growthbegan. The two rounded SLI integrated and covered the surface of the droplet. The corners of the SLI wereobserved in 5 frames.
4.

Discussion
The three-dimensional coordinate of the SLI apex can be obtained by Hough transform and the following

calculations. The radius of the droplet in the image 𝑟 , is the same as that of the actual droplet sphere, 𝑟 . If
the center of the actual droplet is the origin, (𝑥 , 𝑦 , 𝑧 ): the 3D coordinate of the SLI apex is expressed
below as shown in Fig. 2 (c), and Eq. (1).
(𝑥 , 𝑦 , 𝑧 ) = 𝑥 , 𝑦 , 𝑟
where 𝑥𝑎𝑛𝑑 𝑦−𝑥−𝑦(1),are the vector components from the center of the apparent droplet. The included angles 𝜃of two vectors of SLI apex on the specimen were calculated in the equation below as shown in Fig. 2 (d).
𝜃 = 𝑎𝑟𝑐𝑐𝑜𝑠

𝑥 𝑥 +𝑦 𝑦 +𝑧 𝑧,𝑟(2)Where (𝑥 , 𝑦 , 𝑧 ) and (𝑥 , 𝑦 , 𝑧 ) are coordinates of the corners of SLI in former and later images.
Furthermore, the displacement on the droplet surface l, is calculated by multiplying 𝜃 and 𝑟 . Finally, theframe rate f, was multiplied by l to obtain the local crystal growth rate v. The tendency is that the crystal growthrate becomes faster as the crystal grows as shown in Fig. 2 (e). The error of calculation is also shown.

Figure 2. Schematic of calculation. Four plots in (e) come from five frames with corners in view field.

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Conclusions
The images of solidification during recalescence were recorded by the HSC in the ISS-ELF. The coordinatesof the SLI were projected from 2D to 3D and the crystal growth rates of undercooled droplet were calculated.
As a result, it was revealed that the local crystal growth rate increases during recalescence.
Reference1)

D. M. Stefanescu: Morphology of Primary Phases. In Science and Engineering of Casting Solidification, 3rd ed.,Springer (2015).
© 2023 by the authors. Submitted for possible open access publication under theterms and conditions of the Creative Commons Attribution (CC BY) license(http://creativecommons.org/li censes/by/4.0/).
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