Optimization on mechanical properties of Fe7−xCrxC3 carbides by first-principles investigation

► The structural and elastic properties of Fe7−xCrxC3 were investigated using first-principles. ► A new carbide Fe4Cr3C3 was found to be a combination of mechanical properties. ► Strengthening mechanism was analyzed by a new theory. A serious investigation of Fe7−xCrxC3 carbides were performed based on first-principles calculations. Alloy element Cr can enhance the structural stability of Fe7−xCrxC3 carbides. Among Fe3C and Fe7−xCrxC3 carbides, Fe4Cr3C3, which shows a higher elastic moduli, is potentially a high-strength and hard material, possessing a ductile property interestingly as well. Calculated hardness of Fe4Cr3C3 is higher than other carbides which are consistent with the current experiments. Electronic structures show that Fe7−xCrxC3 carbides have complex mixture of metallic, covalent, and ionic characters.