Microstructure Formation during Solidification of Melt-Spun Co-Fe-Mn-Si Alloys

Abstract

Cobalt-based alloys ribbons for the fabrication of cored wires require high elongation, e.g. a good metallurgical quality associated with a fine grain structure. The melt-spinning process allows fabricating the 200 μm thick ribbons in a single casting step. However, the properties of such ribbon suffer from the presence of casting defects, leading to early fractures in the material. The present study investigates the microstructure and defect formation in melt-spun Co-6.5Fe-2.6Mn-(0-1.6)Si alloys (in wt.%). These alloys exhibit uncommon intrinsic behaviour and properties such as high nucleation undercoolings (up to 295K in DTA experiments) or reduced solidification interval (10 < T0 < 25 K). It is found that the main defect leading to fracture is micro-shrinkage due to the solutal dendrite growth at low nucleation undercooling. Low silicon additions (0.6 wt.%) are found to reduce the size and the occurrence of shrinkage and increase the elongation, whereas larger silicon additions (1.6 wt.%) are detrimental to the ribbon properties.