Materials Frontier No.144
Title: Recent Progress: In-situ Observation of Solidification in Metallic Alloys
Speaker: Professor Hideyuki Yasuda
Department of Materials Science and Engineering, Kyoto University，Yoshida-Honmachi, Sakyo, Kyoto, 606-8501, Japan
Inviter: Prof Jun WANG
1986.3. Bachelor, Department of Materials Science and Engineering , Faculty of Engineering,KyotoUniversity
1991.3. Dr.Eng., Department of Materials Science and Engineering,GraduateSchoolof Engineering,KyotoUniversity
1991.3. Doctor of Engineering,KyotoUniversity
1991.4.- Assistant Professor, Department of Materials Science and Processing,OsakaUniversity
1993.5-9. Visiting Scholar, The University ofNottingham,UK
1994.5-9. Visiting Scientist, Massachusetts Institute ofTechnology,USA
1997.2.- Associate Professor, Department of Materials Science and Processing,OsakaUniversity
1997.4.- Associate Professor, Department of Adaptive Machine Systems,OsakaUniversity
2004.4.- Professor, Department of Adaptive Machine Systems,OsakaUniversity
2013.4.- Professor, Department of Materials Science and Engineering,KyotoUniversity
In-situ observation of solidification in metallic alloys
Hideyuki Yasuda1, Tomoya Nagira2, Masato Yoshiya2,
Kohei Morishita1, Kentaro Uesugi3
1 Department of Materials Science and Engineering,KyotoUniversity
2 Department of Adaptive Machine Systems.OsakaUniversity
3 JASRI / SPring-8
Recently, the synchrotron radiation X-rays has arrowed us to observe solidification of metallic alloys in-situ. This presentation will give a brief review of the X-ray imaging we have developed in SPring-8 (Japnese synchrotron radiation facility). The brief review will be followed by the solidification of steels, the deformation of semisolid and the melt convection induced by the static magnetic field.
(a) δ/γ transformation in Fe-C alloys
In solidification of steels, it has been considered that the γ phase (fcc) was produced through the peritectic reaction between the δ phase (bcc) and the liquid phase. Time-resolved X-ray imaging was performed to observe the transformation from the δ phase to the γ phase in Fe-C alloys (up to 0.45 mass%C). Two different transformation manners were identified. One is the peritectic reaction in which the γ phase is produced in the mushy region (δ+L). The other is the massive-like transformation in which the δ phase directly transforms into the γ phase. In the observation conditions, the massive transformation was dominantly selected. The observation indicated that the nucleation of the γ phase was rather difficult and the δ phase continued to solidify even below the peritectic temperature. As a result, the solid δ phase massively transformed into the γ phase in a short period (<1s).
(b) Deformation of semisolid
In-situ observation was carried out to observe shear deformation of semi-solid Fe-2C steel by using synchrotron X-ray radiography. Samples with globular morphology and effective solid fractions of 55-65% were deformed at a rate of ~10-3 s-1. Deformation was predominantly controlled by the rearrangement of globules. The solid particles were pushed each other and the rearrangement caused the lower solid fraction region in the shear deformation. Thus, the interaction between the solid particles is a key issue for understanding the segregation band induced by the shear deformation. On the basis of the in-situ observation, a macroscopic model is introduced to simulate the deformation and the segregation.
(c) Convection induced by the static magnetic field
Imposition of magnetic field during solidification can cause various phenomena. For example, it has been well know that the static magnetic field reduces melt flow. However, it has been pointed out that the magnetic field can agitate melt flow in the mushy region due to the thermoelectric magnetic convection. Time-resolved and in-situ X-ray imaging was performed for unidirectional solidification of Al-Cu alloys. Melt flow in and near the mushy region was detected by observing movement of detached arms. In the case of 0T, the detached dendrite arms moved upward due to the buoyancy force, indicating no intense convection. In the case of 0.45T, the detached arms moved horizontally. The velocity of detached arms was as high as 300μm/s. The motion clearly proved that the convection was induced by imposing the static magnetic field.