First principle investigation of Mo substitution on the structural mechanical and thermal stability of TiMoB2 solid solutions

Titanium diboride (TiB₂) and molybdenum diboride (MoB₂) are known for their excellent mechanical properties such as high hardness, wear resistance and thermal stability, of great interest in advanced engineering applications. This study systematically explored the structural, electronic, thermal, and mechanical properties of Ti-Mo-B₂ solid solutions via first-principles density functional theory (DFT). Mo is substituted into the TiB₂ lattice to investigate its effect on five alloy compositions of key material properties. Our analysis revealed that increasing Mo content enhances ductility while reducing stiffness and hardness, transitioning from a more rigid, covalent structure in TiB₂ to a more ductile, metallic behavior in MoB₂, as shown by the rise in Poisson's ratio from 0.13 in TiB₂ to 0.26 in MoB₂ and the Pugh's ratio increase from 1.00 to 1.70. Mo substitution reduces Debye temperature as well as melting points. Phonon dispersion calculations show that the Ti_0.5Mo_0.5B₂ solid solution exhibits dynamical stability, making it a promising composition for enhanced mechanical and thermal stability. Our studies also demonstrate that the alloys form stable solid solutions across all compositions, with stability reflected by negative mixing energies. These findings provide a key information into designing high-performance Ti-Mo-B₂ composites with specific mechanical and thermal characteristics.