Hard and tough sub-stoichiometric B1 Ta-Mo-Nx films by regulating N content

Abstract

Ternary transition metal nitrides (TMNs) films with B1 structure (NaCl type) have been widely explored as hard protective materials. Their structure and mechanical performances are influenced by the stoichiometric coefficients (TM: N), while the films with high hardness yet sound toughness could be obtained by regulating the nitrogen content. In this case for the sub-stoichiometric B1 Ta-Mo-Nx films, the microstructure, mechanical properties and the toughening mechanisms by N atoms were investigated. The NaCl-structure sub-stoichiometric Ta0.44Mo0.56Nx films with N concentrations at 0.42 ≤x ≤ 0.73 grown by reactive magnetron sputter deposition. The film with x = 0.59 shows higher hardness (∼36.4 GPa), combined with shorter cracks around indentation and higher scratch resistance, reveals the enhanced fracture toughness (KIC=∼1.67 MPa*m1/2, H/E = 0.14); the film simultaneously obtained a lower wear rate (∼6.6 × 10−7 mm3/N * m) and friction coefficient (∼0.4). The formed point defects in sub-stoichiometric Ta-Mo-Nx films are responsible for the enhanced toughness, while the film with x = 0.59 exhibit an increased p(N) - d-eg(Me) strength character accompanied with high d-t2 g(Me) - d-t2 g(Me) metallic states for the TM-N bonds according to the XPS results.