S.B. Luo

Liquid phase separation and rapid dendritic growth of highly undercooled ternary Fe62.5Cu27.5Sn10 alloy

The phase separation and dendritic growth characteristics of undercooled liquid Fe62.5Cu27.5Sn10 alloy have been investigated by glass fluxing and drop tube techniques. Three critical bulk undercoolings of microstructure evolution are experimentally determined as 7, 65, and 142 K. Equilibrium peritectic solidification proceeds in the small undercooling regime below 7 K. Metastable liquid phase separation takes place if bulk undercooling increases above 65 K. Remarkable macroscopic phase separation is induced providing that bulk undercooling overtakes the third threshold of 142 K. With the continuous increase of bulk undercooling, the solidified microstructure initially appears as well-branched dendrites, then displays microscale segregation morphology, and finally evolves into macrosegregation patterns. If alloy undercooling is smaller than 142 K, the dendritic growth velocity of γFe phase varies with undercooling according to a power function relationship. Once bulk undercooling exceeds 142 K, its dendri...

Liquid phase separation and subsequent dendritic solidification of ternary Fe35Cu35Si30 alloy

Abstract Liquid Fe35Cu35Si30 alloy has achieved the maximum undercooling of 328 K (0.24TL) with glass fluxing method, and it displayed triple solidification mechanisms. A critical undercooling of 24 K was determined for metastable liquid phase separation. At lower undercoolings, α-Fe phase was the primary phase and the solidification microstructure appeared as homogeneous well-defined dendrites. When the undercooling exceeded 24 K, the sample segregated into Fe-rich and Cu-rich zones. In the Fe-rich zone, FeSi intermetallic compound was the primary phase within the undercooling regime below 230 K, while Fe5Si3 intermetallic compound replaced FeSi phase as the primary phase at larger undercoolings. The growth velocity of FeSi phase increased whereas that of Fe5Si3 phase decreased with increasing undercooling. For the Cu-rich zone, FeSi intermetallic compound was always the primary phase. Energy-dispersive spectrometry analyses showed that the average compositions of separated zones have deviated substantially from the original alloy composition.

Rapid Solidification Processing of Ag-5%Bi Alloy under Microgravity Condition inside Drop Tube

Liquid Ag-5%Bi alloy has been rapidly solidified in the form of 84-1140 μm droplets under free fall condition. The results show that there are dendritic (Ag)1 phase, interdendritic (Ag)2 phase and (Bi) solid solution phase in this alloy respectively. The microstructure of (Ag)1 phase displays a conspicuous “dendritic-equiaxed” morphology transition with the decrease of droplet diameter, which is attributed to the fragmentation of dendrites induced by the recalescence of highly undercooled liquid alloy. The theoretical analysis with the LKT/BCT dendritic growth model predicts that the growth velocity of (Ag) dendrite increases with undercooling, and the kinetics transition from solute diffusion-controlled growth to thermal diffusion-controlled growth occurs at 98 K during solidification. Meanwhile, the remarkable solute trapping effect takes place according to theoretical calculated calculation.