Integrative approach to enhance the soft magnetic properties of Co35Cr5Fe10Ni30Ti20-xAlx (x= 10, 15, 20) high entropy alloys

Abstract

High Entropy Alloys (HEAs) are advanced materials having multi-functional properties. These materials have the potential to overcome the shortcomings of conventional soft magnetic alloys. In this study, an integrative approach is adopted to enhance the magnetic and electrical properties of CoCrFeNiTi-based HEA by the addition of Al in different content for Ti and annealing for different temperatures and durations. Firstly, Co35Cr5Fe10Ni30Ti20-xAlx (x= 10, 15, 20) HEAs were synthesized through mechanical alloying and investigated for phase formation and magnetic properties. Major fcc with minor bcc and intermetallic R phase has formed for Co35Cr5Fe10Ni30Ti10Al10 and Co35Cr5Fe10Ni30Ti5Al15 HEAs. However, the mixture of fcc and bcc phase with a minor fraction of σ phase has been found for Co35Cr5Fe10Ni30Al20 HEA. The value of Ms is slightly decreased for Co35Cr5Fe10Ni30Ti5Al15 HEA as compared to Co35Cr5Fe10Ni30Ti10Al10 HEA, but for Co35Cr5Fe10Ni30Al20 HEA, the value of Ms has drastically decreased when Ti completely removed for Al. Among these three synthesized HEAs, the highest value of Ms is found for Co35Cr5Fe10Ni30Ti10Al10 HEA (Ms=78 emu/g). Further, we investigated the effect of annealing at different temperatures for 2 h on phase evolution, microstructure, and their correlation with magnetic properties of Co35Cr5Fe10Ni30Ti10Al10 HEA. Among annealed HEA, 700°C annealed Co35Cr5Fe10Ni30Ti10Al10 HEA has high Ms (104 emu/g), and the value of Hc was found to be 29 Oe. The long-duration annealing is also performed at 700°C for 10 h to improve the magnetic properties of the as-synthesized Co35Cr5Fe10Ni30Ti10Al10 HEA and found good soft magnetic behaviour (Ms=103.5 emu/g and Hc=13 Oe). Moreover, the electrical resistivity of the long-duration annealed Co35Cr5Fe10Ni30Ti10Al10 HEA is also recorded in the temperature range 2–350 K, and the value of electrical resistivity at 2 K and 300 K is found to be 180.2 ×102 µΩ.cm and 200.80 ×102 µΩ.cm, respectively. The found value of electrical resistivity is the highest value of resistivity reported so far in the case of soft magnetic HEA.