Effect of annealing conditions and temperatures on phase formation and magnetic behaviour of CrFeMnNiTi high entropy alloy

Abstract

An equiatomic CrFeMnNiTi high entropy alloy (HEA) was synthesized through mechanical alloying (MA) technique. The synthesized HEA consists of FCC, BCC and a minor σ-phase. In order to investigate the phase evolution and magnetic characteristics, the synthesized HEA was annealed under different conditions (vacuum and open air) at two different temperatures (500 and 700 °C). After vacuum annealing at 500 and 700 °C the volume fraction of FCC and BCC phases are changed. However, after open air annealing, the volume fraction of synthesized phases (FCC and BCC) is altered effectively along with the formation of an oxide (Mn2O3) and a spinel type (Fe,Ti)3O4 phase. The synthesized sample exhibits ferromagnetic characteristic and the value of saturation magnetization (Ms) and coercivity (Hc) are found to be 13.39 emu/g (A-m2/kg) and 162.2Oe (12.9 × 103 A/m) respectively. After annealing in vacuum and open air at 700 °C the value of Ms. is found to be 2.95 and 11.63 emu/g (A-m2/kg) respectively. Open air annealed sample at 500 °C shows better magnetic characteristics with Ms = 32.85 emu/g (A-m2/kg) and Hc = 159.34Oe (12.67 × 103 A/m) as compared to the synthesized and annealed samples. The enhanced value of Ms for open air annealed HEA at 500 °C corresponds to increase in the volume fraction of BCC phase and the formation of Mn2O3 and (Fe,Ti)3O4 spinel phase. The effect of annealing conditions on the phase formation and their correlation with magnetic characteristic are discussed and described in detail.