Study of microstructure and magnetic properties in transition metal-based High Entropy Alloys

Abstract

Alloys have played a major role in the development of human civilization. Earlier, they were made with a combination of around two metals. In this work High Entropy Alloys (HEAs) were studied which are the combination of five or more than five elements. Alloy-1 (Fe0.25Co0.25Ni0.25Cr0.25) has four elements, which act as a base alloy. It satisfies the definition of a Medium Entropy Alloy (MEA) with 𝛥𝑆mix around 1.3 R. Mn, Ge, and Si were added, which formed alloy-2 (Fe0.2Ni0.2Cr0.2Co0.11Mn0.11Ge0.9Si0.9). This alloy satisfies the definition of High Entropy Alloys with 𝛥𝑆mix ~ 1.8 R. It was found that alloy-1 shows a dominant FCC phase. Two peaks were undetermined in the XRD of alloy-1. Still, the FCC phase is dominant. It was further found that the BCC phase in alloy-2 is the dominant phase, with one undetermined peak, which may be there due to the formation of the intermetallic (IM). SEM micrographs show the columnar grains in alloy-1 and dendritic formation in alloy-2. From the EDS data, it was found that all the elements in alloy-1 were found to be equally distributed, forming a solid solution. In alloy-2, segregation of Si was found to be in and around the interdendritic region. The hardness of the system drastically increased from around 130 HV0.5 in alloy-1 to around 640 HV0.5 in alloy-2. It was attributed to the presence of Si and Ge, as they have different atomic sizes compared to other elements. At last, the magnetic properties of both systems were studied with the help of VSM. It was found that alloy-1 showed paramagnetic properties at room temperature, and alloy-2 showed soft-ferromagnetic properties at room temperature.