Analysis Method for Ti and Ti-6Al-4V Crystal Growth Rate with High-Speed Camera at the ISS-ELF

抄録

This paper proposes a methodology to determine and validate the local crystal growth rate for vertices of the solid-liquid (S-L) interface at each frame. The crystal growth in levitated Ti and Ti-6Al-4V melts was successfully observed for the first time using a high-speed camera (HSC) installed in the electrostatic levitation furnace in the International Space Station. The displacement of the S-L interface vertices on the sample surface per unit time is defined as the local crystal growth rate. The mathematical equations to geometrically calculate the displacement and error sources were derived, and their parameters were acquired via image analyses. Quantification error, lens distortion, and crystal movement were identified as error sources. Subsequently, the equations for evaluating the error sources were derived. According to the proposed method, the quantification error is dominant under the experimental setup used in this study. For all samples, consequent plots without overlapping error bars exist. Therefore, the variations in the local crystal growth rate are significant. The proposed methodology revealed that the local crystal growth rate decreased at first and then increased during both former and latter halves of the solidification process on the sample surface. These changes in the local crystal growth rate can be attributed to the preferred orientation of crystal growth.