OR3-5
Hetero-3D
TiC

Ti6Al4V

Dissolution Phenomenon of TiC Added in Ti6Al4V
in Electrostatic Levitation Experiments for Hetero-3D,,,2,3,4,5,5,5,6,1,Yuji MABUCHI1, Chihiro HANADA1, Yuto UEDA1, Koei KADOI1, Yuta KUSHIYA1, Hirokazu AOKI1,Kanae YONEDA2, Ryosei SAGUCHI2, Motoko YAMADA2, Hisashi SATO2, Yoshimi WATANABE2,Shumpei OZAWA3, Shizuka NAKANO4, Chihiro KOYAMA5, Hirohisa ODA5, Takehiko ISHIKAWA5,Yuki WATANABE6, and Shinsuke SUZUKI1
11,1,1,1,1,2,222, Waseda University,, Nagoya Institute of Technology,, Chiba Institute of Technology,Henry Monitor, Henry Monitor Inc.,, Japan Aerospace Exploration Agency (JAXA),, Advanced Engineering Services (AES)

1.

Introduction
To elucidate the mechanism of prior- grain refinement of Ti6Al4V alloy due to heterogeneous nucleationsite particles (TiC), the space mission Hetero-3D was carried out to melt and solidify the samples in theelectrostatic levitation furnace in the International Space Station (ISS-ELF). However, preliminary experiments
conducted in a ground based electrostatic levitation (ESL) furnace revealed that some TiC particles weredissolved during heating1,2). The objective of this study was to clarify the effect of dissolution phenomenon ofTiC on the prior- grain refinement of Ti6Al4V in the ESL experiments.
2.

Experimental Procedures
Ti6Al4V powder with 5 mass% TiC particles was mixed homogeneously. The powder was sintered by

the spark plasma sintering method and solidified into spherical shapes in a plasma arc melting furnace. Then,each sample was heated using three laser beams in an ESL furnace. The temperature history of the sample wasobtained by a pyrometer. Based on the result in a previous study3) that the diffusion coefficient in liquid metal
is a proportional to a square of its temperature, a parameter of integral value of heating T2t was introduced,
which was calculated by integrating the square of the temperature T2 and the heating time t. The calculation
range was from the sample first reached the melting point of Ti6Al4V (1923 K) until its temperature fell below
1923 K after the laser beams were turned off. Prior- grain maps were obtained by reconstructing crystal
orientation data of the cross-section of the samples measured by an electron back scattered diffraction detector.
In addition to that, images of microstructures were observed with a scanning electron microscope (SEM).
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3. Results
Integral values of heating T2t of the refined samples were smaller than 1.5 × 108 K2s whereas those of thenon-refined samples were larger than that value. The amount of residual TiC was calculated using theequation1) from the area ratio of carbon precipitates. Figure 1 shows that the amount of residual TiC in Ti6Al4V
decreased as T2t increased. Furthermore, more than 1 mass% of TiC remained, and prior- grains were refinedwhen T2t was less than 1.5 × 108 K2s.

Figure 1. Relationship between the integral value of heating and the amount of residual TiC in Ti6Al4V.
The images2) on either side of the graph show the prior-grain map on the top and the SEM image
on the bottom, respectively.

4. Discussion
According to Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation, the solid phase ratio increasesexponentially with the solidification time, and dissolution can be considered as an opposite phenomenon ofsolidification. The fitting curve in Fig. 1 shows that the amount of residual TiC decreases exponentially withincreasing T2t, therefore the symmetry of JMAK equation was established during dissolution of TiC.
5. Conclusions
Dissolution of TiC was suppressed as the integral value of heating T2t decreased, and prior- grains wererefined when T2t was less than 1.5 × 108 K2s. The amount of residual TiC in Ti6Al4V increased exponentiallywith increasing T2t along with the symmetry of JMAK equation.
References1)
2)

3)

Y. Mabuchi, C. Hanada, H. Aoki, S. Suzuki, K. Yoneda, M. Yamada, H. Sato, Y. Watanabe, C. Koyama, H. Oda, T.
Ishikawa, Y. Watanabe, T. Shimaoka, and S. Suzuki: Abstract of JASMAC-33 (2021) P22.
Y. Mabuchi, H. Aoki, C. Hanada, Y. Ueda, K. Kadoi, K. Yoneda, M. Yamada, H. Sato, Y. Watanabe, Y. Harada, S.
Ozawa, S. Nakano, C. Koyama, H. Oda, T. Ishikawa, Y. Watanabe, T. Shimaoka, and S. Suzuki: Abstract of JASMAC34 (2022) P13.
G. Frohberg: Mass transport by diffusion, Fluid Sciences and Materials Sciences in Space, 1st ed., H. U. Walter,Springer-Verlag (1987).
© 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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