Strengthening of cost-effective Co-free medium entropy alloys by Al/C alloying

The effects of the elemental Al or C addition on the microstructure and room-temperature mechanical properties of a cost-effective Cr₁₂Fe₆₀Mn₁₆Ni₁₂ medium-entropy alloy were investigated. The yield stress of a medium-entropy alloy substantially increased from 230 MPa to 458 MPa following the addition of small amounts of elemental Al (∼2.0 at.%) or C (∼1.0 at.%). Throughout experimentation and theoretical modeling, we were able to systematically show that the improvement in the yield stress following the Al/C addition was attributed to the combination of various strengthening mechanisms, such as grain boundary strengthening, precipitation strengtheing, and solid-solution strengthening mainly caused by the lattice distortion or lattice strain. On the fundamental level, this work provides insights into the effect of the lattice constant on the stress increase for both substitutional and interstitial solid-solution strengthening.