Microstructure evolution and mechanical properties of in-situ multi-component carbides reinforced FeCoNi alloy

In-situ carbides dispersion is an effective reinforcement strategy for alloys. However, introducing traditional single-principal element carbides often lead to a severe loss of strength and ductility. Based on the design principle of high entropy alloy, (Fe₄₀Co₅₀Ni₁₀)-(VNbTaZrC_x) alloys strengthened by in-situ high entropy multi-component carbides (MCCs) were fabricated by introducing refractory metal elements (V, Nb, Ta, Zr) and their carbides into FeCoNi alloy via vacuum arc melting. The dispersed MCCs with rock-salt structure was formed in the FeCoNi matrix with BCC structure. At grain boundaries, an irregular lamellar/granular eutectic structure formed composed of BCC-type secondary solid solution and FeCoNi matrix. With the increase of C content, the microstructure of the alloys was refined significantly, and the volume fraction of in-situ MCCs increased while the opposite trend happened in the eutectic structure. Due to the excellent properties of high entropy MCCs combining with the dispersion strengthening and grain refinement strengthening, remarkable strengthening and toughening effects were achieved for the (Fe₄₀Co₅₀Ni₁₀)-(VNbTaZrC_x) alloys. The yield strength, ultimate strength, and elongation of C2 were 787 MPa, 1176.5 MPa, and 6.54%, respectively. Compared with the Fe₄₀Co₅₀Ni₁₀ alloy, the ultimate strength was increased by 90.1% and the elongation was increased by 5 times. The good combination of the strength and ductility was attributed to the dislocation pile-ups and the deformation twins appeared in the MCCs during deformation.