Toughening FeMn-based high-entropy alloys via retarding phase transformation

Various high entropy alloys(HEAs)with improved mechanical properties were developed by reducing the phase stability and then promote the phase transformation.The promotion of deformation-induced ma rtensitic transformation from face-centered cubic(fcc)to hexagonal close-packed(hcp)mostly focuses on overcoming the trade-off of strength-ductility of HEAs at room temperature.However,the hcp phase is brittle at cryogenic-temperature,and thus the enhancement of cryogenic ductility of these HEAs still remains a challenge.Here,we present a concept to toughening Fe50Mn30Co10Cr10 HEAs at cryogenictemperature via retarding phase transformation.The retarded but more persistent phase transformation at high strain level was realized via tailoring the grain size.To further verify the effect of phase transformation rate on ductility of HEAs,the mechanical properties of Fe40Mn40Co10Cr10 HEAs with higher stacking fault energy were tested at room and cryogenic temperature,respectively.The present study sheds light on developing high perfo rmance HEAs,especially for alloys with brittle phase transformation products.