Evolution of microstructure, elemental segregation and magnetic order in Ti20Co20Cu20Fe20Ni20 high entropy alloy

Ti20Co20Cu20Fe20Ni20 HEA was prepared by mechanical alloying and consolidated by spark plasma sintering. The microstructural studies including Atom Probe Tomography and evaluation of magnetic properties suggest partitioning of elements into (Fe, Co, Ni)-rich ferromagnetic δ-phase and non-ferromagnetic µ-phase. Owing to large change of magnetic entropy across the Curie temperature of the ferromagnetic phase, the phase separation becomes more prominent and is evident in the form of clustering of ferromagnetic elements. The presence of alternate lamellae of ferromagnetic δ phase and non-ferromagnetic µ-phase in some grains, led to anti-ferromagnetic interactions amongst ferromagnetic δ lamellae resulting from separation by fine scale non-ferromagnetic spacer (µ lamella). Such antiferromagnetic exchange is also in accordance with similar exchange behaviour in Fe/Cu/Fe and Co/Cu/Co multilayers reported earlier. The co-existence of ferromagnetic and antiferromagnetic order leads to presence of exchange bias as evident in the asymmetric shift in the hysteresis loop of the samples along positive field axis. •Single phase multi-component FCC solid solution (χ-phase) formed after 15 h milling.•Phase separation as alternate µ and δ phase becomes prominent at higher temperature.•The ferromagnetic elements exhibits negligible solubility in Cu/Ti rich regions.•Enhanced magnetic entropy causes more segregation of ferromagnetic elements above Tc.•Anti-parallel coupling of δ through spacer phase µ is evident from exchange bias.