Characterization of rapidly solidified Ni-Si and Co-Al eutectic alloys in drop tube

Containerless solidifications of Ni-Si and Co-Al eutectic alloys were carried out using an 8 m drop tube. Molten alloy ejected into a drop tube was rapidly cooled and solidified during free fall. The microstructures of the rapid solidified alloys were evaluated. It was seen that the microstructures of Ni-Si and Co-Al eutectics change from the lamellar and plate-like eutectic to the anomalous eutectic and needle-like forms with decreasing the sample size, respectively. The values of the enthalpy of fusion and specific heat were determined by means of differential scanning calorimetry (DSC) during the transformation from liquid to the solid state. The microhardness of rapid solidified alloys was measured by using a microhardness test device. According to the present measurements, the values of microhardness (HV) for rapid solidified Ni-Si and Co-Al eutectics alloys increase with decreasing the eutectic spacing. (C) 2009 Elsevier B.V. All rights reserved.