Investigation of the phase composition, structure, and properties of multilayer vacuum-arc nanocrystalline Ti-Mo-N coatings

Abstract

Experiments have been made to investigate the influence of layer thickness and production conditions on the phase composition, structure and mechanical characteristics (hardness and modulus of elasticity) of vacuum-arc multilayer nanostructural coatings TiN-Mo2N. It is shown that at a small layer thickness (≈2 nm) an epitaxial growth of isostructural cubic modifications of titanium nitride and molybdenum nitride is possible without two-phase state formation. At a greater thickness, a two-phase material is formed, where the second phase is presented by high-temperature cubic-lattice molybdenum nitride γ-Mo2N, which is isostructural with respect to titanium nitride. A growth in layer thickness from 2 up to 20 nm increases the thermal stability of mechanical properties of these coatings at high-temperature annealings (800 °C). For the whole 2 ÷ 20 nm range of layer thicknesses, high-temperature annealings do not cause changes in the phase composition of coatings, leaving molybdenum nitride in the metastable γ-Mo2N state with a cubic lattice. The reason for γ-Mo2N state stimulation at deposition and γ-Mo2N stabilization at annealing lies in the influence of the second constituent of the multilayer system, viz., titanium nitride (TiN), which has a high binding energy between metal and nitrogen atoms, and also, has the type of the crystal lattice corresponding to γ-Mo2N.