Effect of Ta addition on solidification characteristics of CoCrFeNiTa_x eutectic high entropy alloys

Effect of Ta addition on solidification characteristics of CoCrFeNiTa_x (x = 0.1–0.7) eutectic high entropy alloys were investigated. With increasing Ta content, CoCrFeNiTa_x alloys changed from hypoeutectic alloys with primary γ phase to eutectic alloy (x = 0.43) and to hypereutectic alloys with primary Laves phase. Consequently, Ta content in primary phase significantly increased, while the content of Ta element in γ/Laves eutectic phases slightly decreased. Meanwhile, the solidification path and solidification characteristic temperatures of CoCrFeNiTa_x alloys both agreed with typical binary eutectic phase diagram, and obvious microsegregation of Ta element was only found in CoCrFeNiTa_0.1 alloy. Furthermore, the contents of Co, Cr, Fe and Ni elements in primary phases and distribution behaviors of Co, Cr, Fe and Ni elements were both different in CoCrFeNiTa_x alloys, which indicated that CoCrFeNiTa_x alloys cannot be simplified as (CoCrFeNi)–Ta pseudo binary system when analyzing distribution behaviors of Co, Cr, Fe and Ni elements.