Trends in structural, electronic and elastic properties of Ti2AC (A = Al, Zn, Cu, Ni) based on late transition metals substitution

Recently, the substitutional incorporation of late transition metals in the "A" sublattice of MAX phases further extends the physical properties and diversity of this class of materials. In this study, the structural, electronic and elastic properties of Ti2AC (A = Al, Zn, Cu, Ni) were investigated using the density functional theory. The calculated results reveal that a large number of d orbital bands of Zn, Cu, and Ni atoms accumulate around -6.5 eV, -2.5 eV, and -2.0 eV, respectively, leading to stronger ionic and metallic characteristics for Ti2ZnC, Ti2CuC, and Ti2NiC. Three Ti2AC (A = Zn, Cu, Ni) phases are ductile and consequently damage tolerant, whereas Ti2AlC is brittle in nature. When Al is replaced by Zn, Cu, and Ni, there is a remarkable decrease of hardness and shear modulus, indicating high machinability. Ti2ZnC, Ti2CuC, and Ti2NiC are expected to be promising thermal barrier coating materials.