First-principles study of mechanical, electronic properties and anisotropic deformation mechanisms of TiB under uniaxial compressions

Abstract

TiB is an excellent reinforcement in the titanium matrix, but its deformation mechanism is not clear and this limits the improvement of its performance. To uncover the deformation mechanism, first-principles methods based on density functional theory were carried out to study the mechanical, electronic properties and deformation behaviors of TiB under uniaxial compressions along different axis. The compressive strength along b-axis is the highest, because the B–B bond, which has the highest strength, is along b-axis. Meanwhile, strong anisotropy in TiB structure was observed. Under a-axis compression, the breakage of Ti1–Ti3 (Ti4–Ti2) bonds and the formation of Ti1–Ti4 (Ti3–Ti2) bonds are the main deformation mechanism. When the compression is along b-axis, the breakage of Ti1–B1 (Ti2–B2) bonds as well as the formation of Ti3–B3 (Ti4–B4) bonds cause the stress fluctuation without destroying the structure. Then, the reformation of Ti1–B1 (Ti2–B2) bonds causes the sudden drop in stress. Under c-axis compression, the breakage of the zig-zag B–B chains is the main reason for structural failure. Moreover, there still exists a pseudogap around the Fermi energy after structural failure in b-axis and c-axis compression, in contrast to a-axis compression. Thus, may be, the presence of pseudogap in TiB is originating from the Ti–Ti interaction.