An In-Situ Diagnostic Study of Electromagnetic Stirring Effects on Peritectic Solidification Kinetics for Containerlessly Processed Liquid Fe-Ti Alloys

摘要

The electromagnetic stirring (EMS) effects on peritectic solidification kinetics of undercooled liquid Fe-Ti alloys have been investigated by electrostatic levitation(ESL) and electromagnetic levitation (EML) methods assisted with in-situ diagnostic techniques. The high-sensitivity pyrometer and high-speed camera were employed to monitor the complete solidification process for levitated liquid Fe59Ti41 alloy in undercooling Delta T range of 0 K to 213 K. Theoretical calculations showed that there existed EMS inside electromagnetically levitated alloy melts, and the internal fluid flow dynamics depended on levitation height and melt undercooling. As Delta T rised, the primary dendrite growth velocity V increased according to a power function. Meanwhile, the peritectic recalescence degree Delta T-pr and the peritectic recalescence rate R-pr were enhanced gradually, whereas the peritectic recalescence time t(pr) and the peritectic solidification time t(ps) were shortened linearly. The comparison between ESL and EML experiments revealed that the EMS resulted in four respects of influences including (1) dendrite growth effect, (2) concentration field effect, (3) peritectic reaction effect and (4) microstructure evolution effect. In contrast with ESL, the V of Fe50Ti50 alloy measured by EML was slightly larger at small undercoolings, indicating the EMS affected dendrite growth processes. The solute concentration CL around primary Fe2Ti dendrites for electrostatically levitated liquid Fe59Ti41 alloy deviated far away from original composition, while the EMS homogenized concentration field and the CL variation was weak under EML condition. Both t(pr) and t(ps) in the absence of EMS were longer that those in the presence of EMS, and it was demonstrated that the EMS accelerated peritectic reaction. Except for microstructure refinement, the EMS modulated the microstructure type and also changed the faceted-growth mode of intermetallic compound phases.