Elastic Constants and Related Properties of Ti4AC3 (A = Si, Au, Ir) MAX Phases: A Comparative First-Principles Study

MAX-phase materials exhibit metallic–ceramic properties. The Ti4AC3 (A = Si, Au, Ir) 413-type MAX phases are investigated here using systematic density functional theory to examine structural stability, elastic behavior, mechanical performance, thermal properties, and electronic characteristics. Optimized lattice parameters agree with existing theoretical and experimental data. Single-crystal elastic constants satisfy the Born criteria, confirming mechanical stability. Using the Voigt–Reuss–Hill method, polycrystalline moduli are derived: Ti4IrC3 has the highest bulk modulus (B = 227.7 GPa), and Ti4SiC3 has the largest shear modulus (G = 148.1 GPa) and Young’s modulus (E = 354.5 GPa). Ti4AuC3 shows lower moduli, indicating greater ductility (ν = 0.293; G/B = 0.481). Elastic anisotropy is significant in all three phases, with Ti4AuC3 being the most anisotropic. Electronic density of states analysis reveals strong Ti–C covalent bonding that underpins stiffness, while A-site bonding (Si, Au, Ir) influences ductility and anisotropy. This comprehensive comparison elucidates the structure–property relationships of Ti4AC3 (A = Si, Au, Ir) MAX phases and supports their design for targeted applications in aerospace, energy, and mechanical engineering.