Suppression of σ-phase in nanocrystalline CoCrFeMnNiV high entropy alloy by unsolicited contamination during mechanical alloying and spark plasma sintering.

CoCrFeMnNiV high entropy alloy (HEA) exhibits a high content of σ-phase (70 vol%) when produced by casting route. In the present work, a combination of mechanical alloying (MA) and spark plasma sintering (SPS) has been used to synthesize nanocrystalline CoCrFeMnNiV HEA where the formation of σ-phase has been avoided. Electron microscopy and atom probe tomography analysis indicated the formation of FCC structured HEA matrix along with (Cr,V) carbide (15 vol%) precipitation, without the presence of σ-phase in SPS processed alloy. Gibbs energy vs composition (G-x) diagrams of binary subsystems and possible carbides and oxides substantiate the absence of σ-phase during SPS of CoCrFeMnNiV alloy. Thus, the unsolicited contamination during MA-SPS route proves beneficial in suppressing the complex phase formation. Image 1 • Cast CoCrFeMnNiV shows 71 vol% of sigma (σ) phase enriched in Cr and V. • σ-phase is avoided in nanocrystalline CoCrFeMnNiV formed by MA-SPS route. • Un-solicited contamination of during MA-SPS leads to suppression of σ phase. • Calphad based G vs composition plots are used to explain absence of σ phase. [ABSTRACT FROM AUTHOR]