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Freckle defects can be found in several niobium-containing nickel base superalloys. The freckles in VAR or ESR ingots of 718. 706, 625 and other model alloys were analyzed using Scanning Electron Microscopy (SEM) 1 Energy Dispersive Spectrometry (EDS) and Differential Thermal Analysis (DTA). The compositions and the transformation temperatures of the freckled areas \\ere determined It is found that for most of the alloys the composition and melting temperature of the freckle body usually correspond to a solidification moment when about 70% liquid has transformed into solid. though in some alloys the correspondent volume fraction was found to be higher. Freckle criterion considering the compositional effect is proposed for the evaluation of the freckle potential of allojs. Quantitative calculation results of the alloys using the criterion are presented and discussed in terms of the experimental measurements.

Solidification macro-segregation, particularly in the form of freckles, in nickel base superalloys is the main cause for the limitation of the ingot diameter and melting rate during vacuum arc remelting (VAR) and electro-slag remelting (ESR) process.The critical solidification conditions for freckle formation in Alloy 71 8 were studied by horizontal directional solidification (H-DS) experiments under various solidification conditions, and validated by commercial sized VAR ingots. The tendency for freckle formation in this alloy was evaluated by an expression based on the Rayleigh criterion including solidification rate, thermal gradient in the mushy zone, and solidification front angle to the horizontal plane.In order to systematize the methods to predict proper VAR operating conditions for any alloy and ingot diameter, a solidification simulation approach has been developed based on the results of the above trials.

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Tin(Sn) and its alloys have been attracting attentions as a negative electrode material for sodium-ion secondary batteries with high theoretical capacity (Na15Sn4, ca. 847 mAh/g) and high electromotiveforce. There still remains the issue as regards the discharge capacity decrease with increasing the number of cycles. In order to improve cycle performance, there are many studies such as using Sn-Ni alloy, however, using Sn based alloy as negative electrode materials and it suffer from the disadvantage of lowering of discharge capacity. In this study, a deposition process for making Sn film which consists of amorphous structure for negative electrode of sodium ion secondary batteries utilizing electordeposition from aqueous bath was developed. The effect of additives on the surface morphology and microstructure of Sn film was investigated. Furthermore, we evaluated the effect of amorphous structure in the Sn film on cycle performance of the Sn negative electrode. Sn film has a good cycle characteristic (>50 cycles) and discharge capacity (> 400 mAh/g). Amorphous structure in the Sn film showed a microscopic effect on the volume change by sodiation and desodiation.