A systematic approach for enhancing magnetic properties of CoCrFeNiTi-based high entropy alloys via stoichiometric variation and annealing

Abstract

CoCrFeNiTi-based, Co35Cr5Fe20Ni20Ti20, Co20Cr5Fe35Ni20Ti20 and Co20Cr5Fe20Ni35Ti20 high entropy alloys (HEAs) are synthesized through mechanical alloying (MA). The influence of Co/Cr, Fe/Cr and Ni/Cr content separately on structural and magnetic behavior of CoCrFeNiTi-based HEAs are investigated in detail. Mixture of fcc, bcc and minor fraction of R-phase are evolved for all synthesized HEAs. The synthesized HEAs are annealed at two different temperatures (200 °C and 700 °C) in vacuum. Annealing at 200 °C does not affect the relative volume fraction of the synthesized phases. However, annealing at 700 °C significantly affects the relative volume fraction of the synthesized phases. The value of saturation magnetization (Ms) and coercivity (Hc) for synthesized Co35Cr5Fe20Ni20Ti20, Co20Cr5Fe35Ni20Ti20 and Co20Cr5Fe20Ni35Ti20 HEAs are found to be 45.9 Am2/kg and 1.3 kA/m (16.5 Oe), 41.9 Am2/kg and 7.1 kA/m (89.0 Oe), 31.1 Am2/kg and 3.1 kA/m (39.4 Oe) respectively. Based on the value of Hc, the synthesized Co35Cr5Fe20Ni20Ti20 HEA may be considered as a soft magnetic material, whereas Co20Cr5Fe35Ni20Ti20 and Co20Cr5Fe20Ni35Ti20 HEAs may be considered as semi-hard magnetic material. After annealing at 200 °C, the value of Ms increased approximately two times and Hc remains approximately the same to the respective synthesized HEAs. However, dramatic decrease in Hc is observed for 700 °C annealed Co20Cr5Fe20Ni35Ti20 HEA. The present study describes a systematic approach to enhance the magnetic properties of CoCrFeNiTi-based HEAs through stoichiometric variation (Co/Cr, Fe/Cr and Ni/Cr atomic ratio) and annealing.