Alloying behavior in multi-component AlCoCrCuFe and NiCoCrCuFe high entropy alloys

Multi-component high entropy alloys (HEAs) are observed to form simple solid solutions in contrary to general perception that complex compounds may form in such multi-component equi-atomic alloys. In the present study, alloying behavior was investigated using XRD in AlCoCrCuFe and NiCoCrCuFe equiatomic high entropy alloys synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). Simple FCC and BCC phases evolved after MA, while Cu-rich FCC and sigma (sigma) phases evolved along with FCC and BCC phases after SPS. Further, NiCoCuFe, NiCoCrFe and NiCoFe equi-atomic alloys were investigated to confirm the formation of Cu-rich FCC, and sigma phases. The hardness was observed to be 770 +/- 10 HV for AlCoCrCuFe and 400 +/- 10 NV for NiCoCrCuFe. Phase evolution after MA and SPS indicate that configurational entropy is not sufficient enough to suppress the formation of Cu-rich FCC, and sigma phases, and enthalpy of mixing appears to play an important role in determining the phase formation in high entropy alloys after sintering. (C) 2011 Elsevier B.V. All rights reserved.