The mechanism of ductile-brittle transition in carbon alloyed Fe40Mn40Co10Cr10 medium entropy alloys

In this work, the uniaxial tensile tests were conducted on Fe40Mn40Co10Cr10, (Fe40Mn40Co10Cr10)98.5C1.5, (Fe40Mn40Co10Cr10)96.7C3.3 and 0.4 wt% Ti doped (Fe40Mn40Co10Cr10)96.7C3.3 at 298K, 159K and 77K. Meanwhile, the corresponding deformation microstructures as well as the variations of critical shear stress (τ0) and critical normal stress (σ0) were analyzed to unveil the mechanism of ductile-brittle transition (DBT) behavior in carbon alloyed face-centered cubic (FCC) medium/high entropy alloys (M/HEAs). The results show that DBT behavior featured by drastic reduction of ductility with decreasing temperature indeed occurs in (Fe40Mn40Co10Cr10)96.7C3.3. The slightly increased τ0 and the abnormally decreased σ0 at 77K lead to the premature normal fracture of (Fe40Mn40Co10Cr10)96.7C3.3. Severe dislocation pile-ups near grain boundaries due to significantly reduced deformation twinning at 77K is responsible for the embrittlement of (Fe40Mn40Co10Cr10)96.7C3.3. These findings provide deep insights into DBT behavior of carbon alloyed FCC M/HEAs.