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

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-N-x 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 (similar to 36.4 GPa), combined with shorter cracks around indentation and higher scratch resistance, reveals the enhanced fracture toughness (K-IC=similar to 1.67 MPa*m(1/2), H/E = 0.14); the film simultaneously obtained a lower wear rate (similar to 6.6 x 10(-7) mm(3)/N * m) and friction coefficient (similar to 0.4). The formed point defects in sub-stoichiometric Ta-Mo-N-x films are responsible for the enhanced toughness, while the film with x = 0.59 exhibit an increased p(N) - d-e(g)(Me) strength character accompanied with high d-t(2 g)(Me) - d-t(2 g)(Me) metallic states for the TM-N bonds according to the XPS results. (c) 2022 Elsevier B.V. All rights reserved.