Characterization of cast Ti₃₀Cr₂₀Mo₁₅Zr₁₀Ta₅Nb_20-xFe_x compositionally complex alloys

This study systematically investigates the relationship between the microstructure and performance of two cast Ti₃₀Cr₂₀Mo₁₅Zr₁₀Ta₅Nb_20-xFe_x compositionally complex alloys (CCAs), prepared by vacuum arc melting. In the first alloy with (x = 0.0), 20 at.% Nb was added, resulting in the composition of Ti₃₀Cr₂₀Mo₁₅Zr₁₀Ta₅Nb₂₀ CCA (20Nb), while in the second version (x = 10), a more cost-effective variant was developed by partially substituting Nb with 10 at.% Fe, yielding the composition of Ti₃₀Cr₂₀Mo₁₅Zr₁₀Ta₅Nb₁₀Fe₁₀ CCA (10Fe10Nb). Microstructural analysis showed that both alloys have a dendritic structure, with BCC1 as the main phase and a minor BCC2 phase. Some intermetallic phases, such as ZrCr₂, MoNb, and MoTa, were also observed in the 20Nb alloy. In the Fe-containing CCA, more intermetallic compounds were formed with Zr, Cr, Ta, and Ti. The partial replacement of Nb with Fe in the 10Fe10Nb alloy reduced the intensity of the solid solution phases and promoted the formation of additional intermetallic compounds. The microstructure in both alloys was dendritic, with segregation of high-melting-point elements to the dendritic regions. In terms of mechanical properties, the 20Nb alloy exhibited a lower hardness (584 HV) than 10Fe10Nb (667 HV). The 10Fe10Nb alloy demonstrated a higher Young's modulus of (102.47 GPa), while the 20Nb alloy measured (85.92 GPa). Regarding corrosion resistance in saline solution, the 20Nb alloy provided better corrosion protection than 10F10Nb without hydroxyapatite (HA) addition. However, both alloys showed excellent corrosion resistance in the presence of 3 g of HA inhibitor. The corrosion rate of 20Nb decreased from 39.09 μm/y without HA to 1.94 μm/y with 3 g HA, and that of 10Fe10Nb reduced from 61.84 μm/y without HA to 0.38 μm/y with 3 g HA. This emphasizes the effective interaction between Fe-Nb oxides and the deposited HA. Moreover, the incorporation of Nb promoted the formation and stabilization of a passive layer composed of Nb₂O₅ and NbO₂, while the addition of HA further enhanced the film's thickness and compactness. Concluding, the properties of Ti₃₀Cr₂₀Mo₁₅Zr₁₀Ta₅Nb_20-xFe_x CCAs can be tailored for a specific application through balancing Nb and Fe contents, and lower-cost versions can be produced.