Microstructural evolution and mechanical performance of carbon-containing CoCrFeMnNi-C high entropy alloys

The effect of carbon addition up to 1.84 at.% on the mechanical performance and microstructure of a CoCrFeMnNi high-entropy alloy was studied. Both M23C6- and M7C3-type carbide particles were dispersed in the matrix and at grain boundaries in the cold-rolled and annealed carbon-containing alloy. The decrease of grain size in carbon-containing CoCrFeMnNi was predominantly due to grain boundary pinning by the carbide particles. With the addition of 1.84 at.% carbon, the yield stress of the annealed CoCrFeMnNi alloy increased from 253 to 527 MPa at the expense of its ductility. Carbon atoms strengthened the CoCrFeNiMn with 1.84 at.% carbon by grain size refinement (147 MPa) and enhanced friction stress (127 MPa) associated with interstitial carbon atoms and carbide particles. The strain-hardening rate as well as the yield strength increased at the early stage of deformation with increasing carbon content. Carbon addition had a beneficial effect on the mechanical properties by decreasing the grain size, increasing the friction stress associated with interstitial carbon, and enhancing twin stability.