Phase Evolution and Mechanical Behaviour of Co–Fe–Mn–Ni–Ti Eutectic High Entropy Alloys

Abstract

The current study is aimed to understand the microstructure evolution in Co20Fe20Mn20Ni20Ti20 and Co25Fe25Mn5Ni25Ti20 high entropy alloys (HEAs). The complete X-ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy analyses are carried out to recognize the phases in addition to understand the series of phase development in the presently studied HEAs. For Co–Fe–Mn–Ni–Ti HEAs, at first BCC (β) phase primary dendritic phase is created from the liquid, followed by peritectic reaction to form FCC (α) phase (i.e. BCC (β) + L → FCC (α)). Then the left over liquid undergoes eutectic reaction to form FCC (α) and Ti2(Ni, Co) phases (i.e. L → FCC (α) + Ti2(Ni, Co)). Furthermore, the pseudo quasi-peritectic reactions i.e. L + BCC (β) → FCC (α) +Ti2(Ni, Co) has been proposed based on the microstructure evolution study in case of Co–Fe–Mn–Ni–Ti HEAs. It is important to note that Co–Fe–Mn–Ni–Ti HEAs show eutectics between FCC (α) and Ti2(Ni, Co) phases. The multicomponent Co25Fe25Mn5Ni25Ti20 eutectic HEA shows the retention of high strength at elevated temperature. © 2018, The Indian Institute of Metals - IIM.