Hysteresis-free reactive DC magnetron sputtered TiZrHfVNbTa-xN coatings: Structure and mechanical properties

The study of the structure, composition, and mechanical properties of the reactive DC magnetron sputtering (rDCMS) of compositionally complex TiZrHfVNbTa-xN coatings (x- flow of nitrogen) in a hysteresis-free regime revealed that up to a critical flow, nitrogen concentrations, hardness, and indentation moduli increased approximately linearly and then saturated. The linear part was accompanied by the transition from the bcc toward the fcc structure. The highest hardness of 40 GPa and indentation modulus of 500 GPa were achieved in (near-)stoichiometric TiZrHfVNbTa-xN coatings at x ∼ 5 sccm N₂. These values were 10–15 % higher than those reported in similar nitride coatings produced by rDCMS, arc, and HiTUS. Further increase of nitrogen flow caused degradation of mechanical properties without changes in nitrogen concentrations. The results have been described using a model based on gradual occupancy of the interstitial sites of bcc structure of refractory metals forming an interstitial solid solution at low nitrogen flows followed by a transformation into fcc substitutional solid solution with nitrogen occupying anion sub-lattice at flows above critical flow. The work emphasizes the possibilities of the hysteresis-free DCMS regime in effective control of the structure, stoichiometry, and mechanical properties of the compositionally complex nitride coatings using only nitrogen flow control mode and the potential in widening their property envelope.