Effect of nickel content on the microstructure and hardness of AlCoCrFeNi high-entropy clads on ductile iron

This study investigates the cladding of the ductile iron with AlCoCrFeNix (x = 1, 2.1, 3) high-entropy alloys (HEAs) using tungsten inert gas (TIG). The alloy design aimed to create a composite microstructure with complementary phases. Nickel was added to ensure a eutectic solidification path and to stabilize the ductile FCC phase in the matrix. Simultaneously, carbon originating from the ductile iron substrate dissolved into the melt zone, promoting the in-situ formation of the hard carbide phases. The collaboration between the FCC matrix and hard carbides aimed to improve hardness while minimizing embrittlement. Microstructural analysis revealed a dual-phase BCC (B2)/FCC structure in all clad layers, featuring dendritic and inter-dendritic regions. This dual-phase structure was observed in the Ni1 and Ni2.1 HEA clads as a eutectic structure, whereas increased nickel content in the Ni3 HEA clad led to the FCC phase dominance. Substrate dilution also introduced iron into the clad layers, facilitating the formation of the sigma (σ) phases, which enhanced hardness. Hardness measurements showed variations across the clads, with Ni1 (412 HV 0 . 1 ), Ni2.1 (384 HV 0 . 1 ), and Ni3 (409 HV 0 . 1 ), reflecting their distinct microstructural phases. The higher hardness in Ni1 was attributed to its large BCC phase fraction, while in Ni3 , increased dilution promoted carbide and σ-phase formation, contributing to hardness elevation.