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

Abstract

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 high-strength, high-elongation and high-hardness.