Solid solubility extension and nano-mechanical properties of rapidly solidified Fe-Zr eutectic alloys under free fall condition

The liquid-solid phase transitions and solidified microstructures of highly undercooled Fe-Zr eutectic melts were investigated by the drop tube technique. The quantitative relationships among droplet diameter (D), undercooling (Delta T) and cooling rate (R-c) were calculated for three types of eutectic alloys (Fe-9.8 at. % Zr, Fe-6 at. % Zr and Fe-16 at. % Zr alloys). Furthermore, the evolutions of solidified microstructure with droplet diameter were studied. The results show that the eutectic microstructure for Fe-9.8 at. % Zr droplet transforms from regularly lamellar shape to anomalous shape as the diameter reduces. The alpha-Fe dendrite in Fe-6 at. % Zr droplet transforms from coarse dendrite to refined dendrite with the decrease of droplet diameter, while the Fe2Zr dendrite in Fe-16 at. % Zr droplet transforms from faceted dendrite to non-faceted grain. Besides, a remarkable solid solubility extension was found in both the alpha-Fe dendrites of Fe-6 at. % Zr alloy and the Fe2Zr dendrites of Fe-16 at. % Zr alloy. The solid solubility of the alpha-Fe dendrite increases from 3 at. % to 5.6 at. % when the droplet diameter reduces from 1069 to 212 mu m, while it decreases from 31 to 22 at. % in the Fe2Zr dendrite as the diameter reduces from 991 to 228 mu m. The microstructural morphology and solid solubility are directly related to the nano-hardness and Young's elastic modulus of alloys. The nano-mechanical properties of the eutectic gradually increase with the refinement of the layers, and gradually decrease as the irregularity of the anomalous eutectic increases. With the reduction of droplet diameter, the nano-hardness rises and Young's elastic modulus continuously diminishes for the alpha-Fe dendrite due to the increase in the solute content of Zr, while these two mechanical properties gradually decrease for the Fe2Zr dendrite because of the reduction in the solute content of Zr. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The liquid-solid phase transitions and solidified microstructures of highly undercooled Fe-Zr eutectic melts were investigated by the drop tube technique. Quantitative relationships among droplet diameter, undercooling, and cooling rate were calculated for different eutectic alloys. The evolution of solidified microstructure with droplet diameter was studied, showing changes in the microstructural morphology and solid solubility, affecting the nano-mechanical properties of the alloys.