Cr-driven σ-phase formation and microstructural evolutions in TIG-cladded Fe2CoCrxNiMo0.7 high-entropy alloys

In this study, Fe 2 CoCr x NiMo 0.7 (x = 1, 1.5, 2) high-entropy alloys (HEAs) were deposited on AISI 304 stainless steel substrates via tungsten inert gas (TIG) cladding. Elemental powders were proportioned to compensate for substrate dilution (30-38%), ball-milled for 2 h for homogeneity, mixed with PVA binder, and pre-placed on the substrate surface prior to cladding. X-ray diffraction analysis revealed that all Fe 2 CoCr x NiMo 0.7 HEA claddings consisted of an FCC matrix with -phase constituents. In the Fe 2 CoCr 1 NiMo 0.7 cladding, both FeMo-rich and CrMo-rich -phase regions were identified, whereas increasing the Cr content progressively intensified the CrMo-rich -phase reflections. Microstructural observations showed that the Fe 2 CoCr 1 NiMo 0.7 and Fe 2 CoCr 1.5 NiMo 0.7 claddings exhibited dendritic/inter-dendritic structures with Mo enrichment in the inter-dendritic regions, whereas the Fe 2 CoCr 2 NiMo 0.7 cladding developed a hypereutectic microstructure consisting of primary -phase and a + FCC eutectic structure. Microhardness increased markedly with Cr content, reaching surface values of 450 HV (x=1), 505 HV (x=1.5), and 795 HV (x=2). The hardness enhancement is attributed to the combined effects of solid-solution strengthening and, more importantly, the increasing fraction and continuous network of the hard -phase.