Matej Fekete

CrHfMoTaW–N high-entropy nitride thin films were deposited by reactive direct-current (DC) magnetron sputtering and reactive High Power Impulse Magnetron Sputtering (HiPIMS) at ambient temperature and at elevated temperature of 580°C. The influence of HiPIMS pulse parameters, nitrogen flow, deposition mode, and temperature on the phase evolution, microstructure, and mechanical properties of the thin films was systematically investigated. Non-reactive HiPIMS experiments showed that increasing pulse length reduced the effective bombardment while enhancing the contribution of ionised sputtered metal species, leading to phase separation at excessively long pulses. In contrast, increasing the pulse peak current significantly increased the bom- bardment, resulting in denser thin films and modified crystallographic texture. Based on these results, a pulse length of 20 μs and a peak current of 20 A were selected for the reactive depositions. Reactive depositions revealed a strong interplay between thermodynamic effects governed by temperature and kinetic effects governed by ion and neutral bombardment. Increasing nitrogen flow induced a phase transition from metallic bcc structures to fcc nitride phases. Elevated temperature together with high bombardment delayed the bcc–fcc transition and promoted crystallisation and grain growth while also promoting renucleation, and strongly influencing defect formation and crystallite stability. The results further showed that the fcc CrHfMoTaW–N phase is stabilised by nitrogen vacancies. Excessive nitrogen incorporation in ambient-temperature HiPIMS thin films promoted defect formation and limited crystallite growth, while lower nitrogen contents in thin films deposited at elevated temperature enabled continued crystallite growth due to retention of stabilising vacancies. Compared to DC sputtering, HiPIMS deposition resulted in significantly improved mechanical properties, with hardness increases of up to ∼60 % and markedly higher elastic modulus values. The superior properties were attributed to denser microstructure, enhanced crystallinity and larger crystallite size associated with energetic particle bombardment. The results demonstrate that both thermodynamics and ion-bombardment- driven kinetics play essential roles in the formation of refractory high-entropy nitride thin films. Control over both effects enables tailoring of the microstructure, phase composition, and mechanical performance of CrHfMoTaW–N thin films, while HiPIMS represents a highly effective approach for preparing dense and mechanically enhanced refractory high-entropy nitride thin films.

Reactive direct current (DC) magnetron sputtering (rDCMS) and reactive high target utilization sputtering (rHiTUS) of compositionally complex TiZrHfVNbTa–N coatings were systematically investigated with varying nitrogen flow. The study combined experimental measurements of total and partial nitrogen pressures with simulations based on Berg's model. Both deposition systems exhibited hysteresis‐free behavior, characterized by two distinct nitrogen consumption regimes: (1) a nearly linear increase up to a critical nitrogen flow (≈4 sccm in rDCMS and ≈6 sccm in rHiTUS), and (2) a saturation regime. Simulations reproduced these trends and confirmed that hysteresis suppression originates from high pumping speeds (pumping speed/volume ratio > > 4 s ⁻¹ ). The applicability of Berg's model to rHiTUS was validated by the strong agreement between experiments and modeling, supporting the assumption that the fundamental processes of reactive sputtering—target sputtering, poisoning, and nitride formation—are identical in DCMS and HiTUS. The main technological benefit of operating in a hysteresis‐free regime is that coating composition and properties can be controlled solely through nitrogen flow adjustment.