Controllable Preparation And Microstructure Evolution Mechanism Of Undercooled Fe-B-Si Eutectic Alloy

In this paper, a systematic investigation in purification process andmicro-purification mechanism of Fe-B-Si eutectic alloys has firstly been performed,by employing glass slag purification incorporated with cyclic superheatingtechniques.With JMAK equation of coupling catastrophe function being used, therelationship between recalescence curves and solidification structure was studied.With the aid of infrared radiation thermometer, XRD, SEM analytical methods, therapidly solidified structure evolution with undercooling was then systematicallystudied, meanwhile the undercooled Fe-B-Si eutectic alloy interface growth kineticswere highlighted by means of logistic growth model and non equilibrium dendritegrowth model. The main conclusions were as follows:1. The microstructure evolution of undercooled Fe82B17Si1alloy in the obtainedundercooling6K<ΔT<280K were investigated by employing the glass fluxingtechnique in combination with cyclical superheating. When6K≤ΔT<75K, Fe82B17Si1alloy was made of complex rules eutectic and eutectic mixture of quasi regulareutectic; When75K≤ΔT<180K, the solidification microstructure was composed of amixture of eutectic and deeply undercooled irregular eutectic; When180K≤ΔT<250K,the solidification microstructure consists of primary α-Fe phase as well as theirregular eutectic among dendrite; When ΔT>250K, the solidification structure wascompletely non-eutectic organization. With the increase of undercooling, themicrostructure evolution of undercooled Fe82B17Si1alloy gradually by mixing eutecticto irregular eutectic.2. The cooling curves of solidification process were fitted in combination ofbreak equation and JMAK model, and the calculated results were consistent with theevolution of pattern of organization and microstructure of Fe82B17Si1eutectic alloy.The two kinds of mixed eutectic were corresponded to once recalescence curve, whilethe primary α-Fe phase and interdendritic irregular eutectic were corresponded totwice the recalescence curve.3. Based on the recalescence curve, the relationship between undercooling andrecalescence rate (equivalent interface growth velocity) function was extracted,meanwhile with the undercooled Fe-B-Si alloy interface growth, two platforms forgrowth and an exponential growth were found. With the aid of logistic growth modelto fit the relationship curve between recalescence rate and undercooling, it is foundthat two platforms growth corresponded to the formation of two types of granulation tissue, respectively; while exponential growth led to the formation of fine irregulareutectic.