PS25
Hetero-3D の ISS-ELF 実験における Ti-6Al-4V の3 次元結晶粒解析
Three-Dimensional Grain Analysis of Ti-6Al-4Vin the ISS-ELF Experiment for Hetero-3D
門井洸衛 1, 上田雄翔 1, 櫛舎祐太 1, 上野遥か 1, 馬渕勇司 1, 花田知優 1, 青木祐和 1, 左口凌成 2, 山田素子 2,佐藤尚 2, 渡辺義見 2, 小澤俊平 3, 中野禅 4, 小山千尋 5, 織田裕久 5, 石川毅彦 5, 渡邊勇基 6, 鈴木進補 1
Koei KADOI1, Yuto UEDA1, Yuta KUSHIYA1, Haruka UENO1, Yuji MABUCHI1, Chihiro HANADA1,Hirokazu AOKI1, Ryosei SAGUCHI2, Motoko YAMADA2, Hisashi SATO2, Yoshimi WATANABE2,Shumpei OZAWA3, Shizuka NAKANO4, Chihiro KOYAMA5, Hirohisa ODA5, Takehiko ISHIKAWA5,Yuki WATANABE6, and Shinsuke SUZUKI1早稲田大学，Waseda University,
名古屋工業大学，Nagoya Institute of Technology (NITech),
3 千葉工業大学，Chiba Institute of Technology (CIT),
4 株式会社 Henry Monitor，Henry Monitor Inc.,
5 宇宙航空研究開発機構，Japan Aerospace Exploration Agency (JAXA),
6 株式会社エイ・イー・エス，Advanced Engineering Services (AES)
121.

Introduction
To elucidate the amount of TiC acting as heterogeneous nucleation site particles for grain refinement inTi-6Al-4V, Hetero-3D mission was conducted by melting and solidifying samples in the electrostatic levitation
furnace in the International Space Station (ISS-ELF). Due to the limited number of the space experimental
samples, the method to estimate grain counts in the entire sample, N3D, with minimal sample loss was required.
This study aims to propose the method of obtaining N3D from a cross section of the ISS-ELF sample.
2.

Experimental Procedures
Ti-6Al-4V powder with 5 mass% TiC particles was melted and solidified in the ISS-ELF. A sphericalsample with a diameter of 2.26 mm was obtained. A cross section of the sample was obtained by a diamondwire saw and a polishing machine. Furthermore, a prior- grain map of the cross section was obtained by anelectron backscatter diffraction (EBSD) analysis with a step size of 2 m.
The Voronoi tessellation (VT), which divides the regions by perpendicular bisectors as grain boundaries
between preset sites, was conducted to simulate three-dimensional grain distribution using visualization
software, OVITO. Eleven models were generated by VT with various grain counts per volume, NV, from
7 to 333. From each model, cross sections at the same depth as the prior- grain maps were extracted.
Subsequently, the average grain areas on the cross section, 𝐴̅voro , were calculated with dividing grain counts
by the cross-sectional area.
1 of 2

3.

Results
The dimensionless distance from a spherical center to a cross-sectional center, d, was 73 % of sphericalradius. The prior- grain map is shown in Fig. 1(a). Grains on the sample surface, surface-grain, had 0.12 mm²of an average area, 𝐴̅surface . It was six times as large as that of grains not on the surface, inside-grain, with 0.02
mm² of an average area, 𝐴̅inside . The relationship between NV and 𝐴̅voro is shown in Fig. 1(b). The value of NV
decreased exponentially with increasing 𝐴̅voro . Applying 𝐴̅surface and 𝐴̅inside to Fig. 1(b), NV of surface-grain,NV-surface, and inside-grain, NV-inside, were obtained as 10 mm-3 and 285 mm-3 respectively.

Figure 1. Analytical results with the cross sections at 73% of d in the sample and VT models. The
highlighted grains with white and black in (a) indicate surface-grain and inside-grain, respectively.
The graph in (b) shows NV, assuming uniform grain size with the average grain area.

4.

Discussion
Because the sizes between areas of surface-grain and inside-grain were extremely different, the value

averaged for all grains in the cross section should not be uniformly applied to Fig. 1(b). By applying 𝐴̅surfaceand 𝐴̅inside separately to Fig. 1(b), NV was obtained for surface-grain and inside-grain respectively. The equation
summarizing obtaining the grain counts was as follows.
⁄2⁄2
𝐴3𝑠𝑢𝑟𝑓𝑎𝑐𝑒𝐴3𝑖𝑛𝑠𝑖𝑑𝑒𝑁3D = 𝑉sample { 3⁄2𝑁+𝑁𝑣−𝑖𝑛𝑠𝑖𝑑𝑒 }𝑣−𝑠𝑢𝑟𝑓𝑎𝑐𝑒⁄2⁄2⁄2𝐴𝑠𝑢𝑟𝑓𝑎𝑐𝑒 + 𝐴3𝑖𝑛𝑠𝑖𝑑𝑒
𝐴3𝑠𝑢𝑟𝑓𝑎𝑐𝑒+ 𝐴3𝑖𝑛𝑠𝑖𝑑𝑒(1)

where Asurface and Ainside were total area of surface-grain and inside-grain respectively. Eq.1 showed 299 of N3D.
5.

Conclusion
To propose a method for estimating N3D from a cross section of ISS-ELF sample, EBSD analysis and VT

were conducted. By applying Asurface and Ainside from the prior- grain map and NV-surface and NV-inside from NV𝐴̅voro graph to Eq. (1), N3D was estimated to be 299.
© 2024 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/).
2 of 2