This study was designed as a preliminary
experiment for missions at the electrostatic levitation furnace
in the International Space Station (ISS-ELF) such as Hetero-3D.
The objective of this study was to employ a high-speed camera
to determine the recalescence time of undercooled Ti6Al4V
alloy with TiC heterogeneous nucleation site particles more
accurately compared to measurements using a pyrometer. The
sample was melted and solidified in the ground-based
electrostatic levitation (ESL) furnace. The changes in the
luminescence emitted from the sample surface due to
recalescence were recorded using a high-speed camera, and
the intensity at the center of each captured image was analyzed
with MATLAB® software. As a result, the intensity of the
undercooled samples increased significantly during
recalescence. The maximum change in the intensity was 101
per 256 gray levels in the recording at 7,200 frames per second
(fps) and the noise was at most only 3. Therefore, the
recalescence time could be obtained using the high-speed
camera. At 15,000 fps, the recalescence time was within 6.7 ×
10-5 s, which was much more accurate than the time (0.11 s)
measured using a pyrometer at a sampling rate of 120 Hz in the ESL furnace. For enhanced measurement
accuracy, it is crucial to establish an appropriate exposure time to prevent the intensity from reaching the
lower limit of 0 just before recalescence and the upper limit of 255 immediately after that. This study
suggests that the high-speed camera newly installed in the ISS-ELF in 2023 may have the potential to
achieve a more accurate recalescence time than the pyrometer at a sampling rate of 100 Hz in the ISS-ELF.
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