Mechanical and electronic properties of Ti2AlN and Ti4AlN3: a first-principles study

Investigations into the electronic properties, elastic properties, and ideal tensile strengths for Ti2AlN and Ti4AlN3 were conducted using first-principles density functional calculations. The electronic band structures and density of states show metallic conductivity in which Ti 3d states dominate for Ti2AlN and Ti4AlN3. Moreover, the hybridization peak of Ti 3d and N 2p lies at a lower energy than that of Ti 3d and Al 3p, which suggests that the Ti 3d -N 2p bond is stronger than the Ti 3d - Al 3p bond. The variations of elastic constants with pressure indicate that Ti2AlN and Ti4AlN3 possess higher mechanical stability in the pressure range 0-100 GPa. By calculating the bulk-modulus-to-shear-modulus ratio and Cauchy pressure, we predict that Ti2AlN and Ti4AlN3 are brittle. We show that the structural failure of these ternary compounds can be ascribed to the breakage of weak Ti-Al bonds under uniaxial tension and that layered structural stability is determined by the strength of the Ti-Al bond under tensile deformation.