Elastic isotropy originating from heterogeneous interlayer elastic deformation in a Ti₃SiC₂ MAX phase with a nanolayered crystal structure

The elastic properties of a single-crystalline Ti₃SiC₂ MAX phase with a nanolayered crystal structure, comprising Ti-Si and two distinct Ti-C bonding layers, that had remained unclear because of the difficulty in growing large single crystals, were studied. Rather than unavailable large single crystals, polycrystalline samples with a crystallographic texture were prepared. By analyzing the polycrystalline elastic constants on the basis of an inverse Voigt–Reuss–Hill approximation, the elastic properties of a single crystal Ti₃SiC₂ with a hexagonal symmetry were determined. This revealed that the single-crystalline Young's modulus was almost isotropic despite its highly anisotropic layered structure. The shear modulus for (0001)〈112¯0〉 was higher than that for {112¯0}[0001] in contrast to the basal slip-dominated plastic deformation reflecting the layered structure. Furthermore, first-principles calculations revealed that heterogeneous interlayer elastic deformation caused by the stabilization of Ti-Si bonding is the origin of the elastic isotropy in a Ti₃SiC₂ MAX phase.