Investigation of structural and magnetic properties of high entropy alloys by introducing substitutional elements

This study presents how the structural and magnetic properties of high entropy alloys change as a function of valence electron concentration. In the experimental stages, the structural changes of Cr20+xMn20Fe20Co20Ni20-x (x = -2, 0, 2, 5, 10, 15, 20) alloys were measured by X-ray diffraction method and their magnetic properties were measured via superconducting quantum interference device. Temperature dependent magnetization measurements were carried out in the temperature range 10 ≤ T ≤ 380K under 5 mT and 1 T external magnetic field. Magnetic and structural phase transitions in the specified temperature range were investigated. An external magnetic field of 5 mT was used to understand the intirinsic magnetic properties of the alloys, and an external magnetic field of 1 T was used to determine the temperature-dependent magnetic properties under magnetic saturation conditions. In addition, hysteresis loops were obtained in external magnetic fields up to 5 T. As a result of the measurements and investigations, a transition from the face-centered cubic structure to the sigma phase was observed with increasing amount of chromium. The formation of the sigma phase was observed when the valence electron concentration (VEC) reached to 7.73 electrons per atom (e/a). Face-centered cubic and sigma phases coexist in the range of 7.73 and 8.01 e/a. Finally, when the VES reached to 7.12 e/a, the sigma phase was found as a single phase in the microstructure. The increase in the amount of sigma phase in the structure to be in direct proportion to the amount of chromium was supported by hardness measurements. Magnetic properties showed similar behavior in all alloys. According to the measurements made under 5 mT magnetic field, no structural transition was observed between 10 K and 380 K. In addition, mixed interactions resulting from the coexistence of ferromagnetic and antiferromagnetic phases were recorded under an external magnetic field of 5 mT. Alloys with Curie temperatures between 42 and 44 Kelvin have soft magnetic properties below these temperatures.