The correlation between N deficiency and the mechanical properties of the Ti2AlNy MAX phase

The role of X deficiency on the mechanical properties of MAX phases was studied by synthesizing Ti2AlN through powder metallurgy in stoichiometric and sub/extra-stoichiometric nitrogen compositions. XRD analyses and ab initio calculations indicate that nitrogen vacancies result in a lattice contraction predominantly along the c-axis. The elastic moduli and intrinsic hardness of substoichiometric Ti2AlN0.9 measured from nanoindentation tests are shown to be slightly smaller than that of Ti2AlN. The key mechanical indexes, bulk (B), shear (G) and Young’s (E) moduli as well as the hardness variation are calculated in density functional theory, and show different responses depending on the concentration of N vacancies. This joint experimental and theoretical study provides a full understanding of the energetics, chemical bonding, electronic structure, and mechanics of the N deficient MAX phases which would increase the application of nitride ceramics.