**2. Experimental Procedure**

The rapid solidification experiments were performed using the glass fluxing method with a high vacuum chamber. The master alloy of binary Co-4.54%Sn alloy composition was prepared using the arc-melting technique from component metals of high purity above 99.999%. An in situ alloying procedure was applied to prepare about 1 g Co-4.54%Sn alloy using radio frequency induction heating. The sample was contained in an 8 mm ID × 10 mm OD × 12 mm alumina crucible and placed into the experimental chamber, then it was evacuated to a 2 × <sup>10</sup>−<sup>4</sup> Pa vacuum with a turbo pump and subsequently backfilled with argon gas to 10<sup>5</sup> Pa. The sample was superheated to 250~350 K above its liquidus temperature and kept submerged in a pool of molten fluxing agent for 3~5 min. It was naturally cooled down and solidified by switching off the induction heating power. Each sample was subjected to the melting–solidifying cycle 3~5 times. Their heating and cooling curves were recorded using a Land NQO8/15C infrared pyrometer (Sensortherm Gmbh, Steinbach, Germany), while the dendrite growth velocity was measured with an infrared photodiode device (Mikrotron, Unterschleißheim, Germany). The phase constitutions of binary Co-4.54%Sn alloy were analyzed by Rigaku D/max 2500 X-ray diffractometer (XRD) (Rigaku, Tokyo, Japan), whereas their solidification structures and solute distribution profiles were investigated with FEI Sirion electron microscope (SEM) (FEI Sirion, the Netherlands) and INCA Energy 300 energy-dispersive spectrometer (EDS) (FEI Sirion, the Netherlands). The microhardness was measured using an HXD-2000TMC/LCD Vickers hardness tester (Kexin, Beijing, China). The magnetic characteristics was analyzed using a VSM instrument. The resistivity was tested using the four-point probe method.
