Mechanical, electronic properties and deformation mechanisms of Ti<sub>3</sub>B<sub>4</sub> under uniaxial compressions: a first-principles calculation

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As an important Ti-B component, Ti<sub>3</sub>B<sub>4</sub> has been widely used in industry and military applications. However, its deformation behaviors are not clear, which greatly limits its applications. First-principles methods based on density function theory were employed to investigate the mechanical, electronic properties and deformation mechanisms of Ti<sub>3</sub>B<sub>4</sub> under uniaxial compressions along different axis. The results show that the structure underwent a massive change under different axial compressions. Strong anisotropic of deformation behaviors in Ti<sub>3</sub>B<sub>4</sub> was observed. The compressive strength along b-axis is the highest in Ti<sub>3</sub>B<sub>4</sub> structure. Under <i>a</i>-axis compression, the interaction between intralayer Ti—Ti bonds becomes weaker as the compressive strain increases, causing the partly damage of Ti<sub>3</sub>B<sub>4</sub>. However, in this process, the structure is not destroyed and can sustain the stress continuously. After that, the interlayer Ti—Ti bonds and the intralyer B—B bonds which are along <i>b</i>-axis, are broken and then it causes the sudden drop in stress, implying that the Ti<sub>3</sub>B<sub>4</sub> structure is fully destroyed. Under <i>b</i>-axis compression, the changes of Ti—B bonds in Ti<sub>3</sub>B<sub>4</sub> structure lead to the decrease of stress. Similarly, the structure can sustain the stress continuously in the process. Then, the B—B bonds which are along <i>b</i>-axis are broken, resulting in the sudden drop in stress. Under <i>c</i>-axis compression, the formation of interlayer Ti—B bonds and the breakage of intralayer Ti—B bonds result in structural instability of Ti<sub>3</sub>B<sub>4</sub>. Meanwhile, the deformed Ti<sub>3</sub>B<sub>4</sub> still exhibits a metallic feature in the crystalline state after uniaxial compressions. However, there is no noticeable pseudogap in DOS spectra for <i>a</i>-axis and <i>b</i>-axis compressions. While for <i>c</i>-axis compression, there still exists a pseudogap around the Fermi energy, but it moves to the lower energy. And the pseudogap becomes narrower than that of the initial structure, which means that the covalent properties of Ti<sub>3</sub>B<sub>4</sub> are reduced after deformations. The present work provides necessary insights in understanding the mechanical behaviors and deformation mechanisms of Ti<sub>3</sub>B<sub>4</sub>, which is the basis for improving the mechanical performance of Ti<sub>3</sub>B<sub>4</sub> at macroscale.