Hardness augmentation engineering of TiFe<sub>2</sub> with doping design and single-crystal realization

<p>As a critical reinforcing phase in high-entropy alloy matrix and coating materials, enhancing the hardness of TiFe<sub>2</sub> significantly improves the upper limits of alloy performance through low-concentration doping. However, the mechanism by which doping alters macroscopic hardness through the disturbance of electronic structure remains unclear. Furthermore, there is a lack of robust experimental evidence to substantiate the hardness enhancements predicted by theoretical calculations. This investigation assessed the strengthening effect of silicon (Si) on the hardness of TiFe<sub>2</sub> through both calculations and experiments. First-principles calculations indicated that Si alloying enhances the structural stability and hardness of TiFe<sub>2</sub>. The mechanisms underlying the notable increase in hardness due to Si were thoroughly investigated from the perspective of bonding characteristics. Si alloying disrupted the original symmetric electronic structure and increased the prevalence of directional covalent bonds. Successful single-crystal preparation experiments confirmed the stability of the doped structure. The results of nano-hardness testing address the deficiency of accurate experimental data on hardness enhancement. This study provides a systematic approach to improving the mechanical properties of TiFe<sub>2</sub> and offers new insights into the development of advanced materials with enhanced hardness.</p>