Solidification structure analysis of cold crucible directionally solidified Nb-Si based alloy

摘要

The water cooled copper crucible directional solidification was used to prepare Nb-12Si-24Ti-4Cr-4Al-2Hf(at.%) alloy in this paper. An obvious growth trend of directional solidification in the stably solidified area of the sample was observed by scanning electron microscopy(SEM). Microstructure analysis and phases identification of the alloy were examined by X-ray diffraction (XRD), Electro Probe Micro Analyzer (EPMA). The results showed that the phases were composed of Nb solid solution(Nbss), p-Nb5Si3 andy-Nb5Si3 intermetallic phase, and a small amount of Hf02. The volume fractions of P-Nb5Si3 and y-Nb5Si3 were different among the initially solidified area(ISA), the stably solidified area(SSA) and the finally solidified area(FSA). Energy Disperse Spectroscopy(EDS) analysis showed that there was a certain deviation of chemical composition of the initially solidified area, the stably solidified area and the finally solidified area. This may be atributed to that the large thermal conductivity of Nb and the strong lateral heat lead to the low superheat of liquid alloy and the reduction of solute homogenized diffusion process. The technology trend of using water cooled copper crucible directional solidification technology to prepare high-temperature Nb-Si based alloy is to further improve the thermal efficiency of the cold crucible and the temperature gradient of the solid-liquid interface.