Research On Solidification Microstructure Control And Modification Of Faceted-faceted Eutectic Alloy

According to its growth modes, binary eutectic alloys can be classified into three kinds: the nonfaceted-nonfacaeted eutectic (N-N), the nonfaceted-faceted eutectic (N-F), and the faceted-faceted eutectic (F-F). So far, research on the first two kinds of eutectic alloys is sufficient, but research on the faceted-faceted eutectic alloy is rare. In general, the two composed phases of F-F eutectic alloys are intermetallic compound phases. As the intermetallic compound phases have super lattice structure of long range order, and can maintain strong metallic bond, thus they have many special physical, chemical and mechanical properties. Taking advantage of these features, a lot of new kinds of materials have successfully prepared, and can be used for transportation, chemical industry, machinery and many other industrial sectors. However, due to strong anisotropy of the growth of faceted-faceted eutectic alloy, room temperature plasticity is so poor that it is hard to reach processing preparation, thus making it difficult to realize large-scale industrial application.In this paper, the typical faceted-faceted Ni31Si12-Ni2Si eutectic alloy and CoSi-CoSi2eutectic alloy are chosen as the research object. Directional solidification Ni31Si12-Ni2Si eutectic alloy ingots casting were obtained by the method of directional solidification technique combined with vacuum arc melting and, and fracture strength was improved obviously, reaching2100MPa. Directional solidification makes Ni31Si12-Ni2Si eutectic alloy organization evenly and directionally, and reduces the solidification defects, so as to enhance the fracture strength of the eutectic alloy ingot; Big size Ni31Si12-Ni2Si eutectic alloy ingots were obtained by vacuum intermediate-frequency induction with rotating magnetic field, and the ratio of eutectic microstructure was improved, and fracture strength was also improved. But the production efficiency of the method of directional solidification is low, and the size of the ingot is restricted. The modification effect of electromagnetic field is still limited.Finally, CoSi-CoSi2eutectic alloy ingot castings added Ti, Zr, Cu elements were obtained by the method of vacuum arc melting, and research on solidification structure control and modification of CoSi-CoSi2eutectic alloy was carried out. Ni31Si12-Ni2Si eutectic alloy ingot casting added into4wt.%Ti element obtained the maximum fracture strength and reached2051MPa, and it indicates that fracture strength was improved, and compressive plasticity was improved slightly. CoSi-CoSi2eutectic alloy ingot casting added into4wt.%Cu element obtained the maximum fracture strength and reached1303MPa, and it indicates that fracture strength was improved obviously, and compressive plasticity was improved40%.As the solid solubility between trace alloy elements such as Ti, Zr, Cu and Co, Ni and Si element is low, and the binding energy between these alloy elements and Co, Ni and Si elements is also low, it is easier to generate segregation in grain boundary, thus reduces the defects of grain boundary areas. Also because the alloying elements such as Ti, Zr, Cu have good plasticity, during compression deformation, faceted grain extrusive on alloy elements segregation, and it makes sliding smoothly, thus it enhances the fracture strength. This method is beneficial to study on solidification structure control and modification of big size faceted-faceted eutectic alloy, thus it has important theory significance and economic value.