Investigation of microstructure evolution and mechanical properties of near-eutectic Fe2-yCoNiCryCx high entropy cast iron

Near-eutectic Fe2-yCoNiCryCx high entropy (HE) cast iron was designed and characterized. The FeCoNiCrC0.45 eutectic HE cast iron was determined being composed of FCC phase and M7C3 carbide. Their crystallographic orientation relationship at the outer region is [101]//[01 1 0] and {110}//{112 0}. The orientation of eutectic M7C3 carbide changes from [01 1 0] to [123 0] as the grain grows from the outer to inner of sample. With the increase of carbon addition, the alloy composition transits from hypoeutectic to hypereutectic where the primary phase changes from FCC phase to M7C3 carbide. With the increase of chromium addition, the phase constituent transits from a mixture of FCC, M7C3 and graphite to that only with FCC and M7C3. The yield strength, compressive strength and hardness for Fe2-yCoNiCryCx HE cast iron are more sensitive to the chromium than carbon. Fe1.2CoNCr0.8C0.45 HE cast iron exhibits the superior properties with the ultimate strength of 1934 MPa and elongation rate of 21.3%, which is mainly attributed to the strengthening mechanism induced by the precipitation of M7C3 carbide with higher fraction. It provides a clue for the design of new cast iron with highstrength, high-elongation and high-hardness.

Automated summary

This study designed and characterized a near-eutectic Fe2-yCoNiCryCx high entropy cast iron. It was found that the addition of carbon changed the alloy composition from hypoeutectic to hypereutectic, leading to a transition from FCC phase to M7C3 carbide as the primary phase. The addition of chromium transformed the phase constituent from a mixture of FCC, M7C3, and graphite to only FCC and M7C3. The Fe1.2CoNCr0.8C0.45 high entropy cast iron exhibited superior properties with an ultimate strength of 1934 MPa and an elongation rate of 21.3%, mainly due to the strengthening mechanism induced by the precipitation of M7C3 carbide with a higher fraction.