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The structural stability of iridium-based alloys remains significant due to iridium's (Ir) outstanding high-temperature properties and corrosion resistance, particularly for aerospace and extreme-environment applications. However, the inherent brittleness of pure FCC Ir and its high cost limit its broader structural applications. This study employed first-principles calculations based on density functional theory (DFT) to examine the effect of alloying with nickel (Ni) and ruthenium (Ru) on the structural and mechanical stability of Ir using a 2×2×2 supercell method to enable binary substitution in Ir32-x-Mx (M = Ru, Ni). The calculated elastic constants of the investigated Ir32-x-Mx (M = Ru, Ni) binary alloy compositions satisfied the Born-Huang mechanical stability criteria. Cauchy pressure (Cₚ) analysis revealed distinct bonding characteristics: Ru-containing compounds exhibited covalent bonds (Cₚ < 0), while Ni additions ≥ 18.75 at. % displayed metallic bonds (Cₚ > 0), associated with ductility. Poisson's ratio (ν) further validated these trends; for metallic bonding, ν > 0.26, otherwise covalent and brittle. All Ru-containing alloy compositions showed ν < 0.26, indicating brittleness, whereas Ni ≥ 18.75 at. % yielded ν > 0.26, confirming metallic and ductile behaviour. The ductility in the latter was further supported by the calculated Pugh's ratio (B/G) ≥ 1.75. Similarly, the Ru-containing alloy compositions maintained brittleness as evidenced by B/G < 1.75).
Keywords: Iridium, brittle character, density functional theory, elastic properties, ductility
| Apply for student award at which level: | MSc |
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