PVD COATING TREATMENT TOWARDS A SUSTAINABLE AND ECO-FRIENDLY MANUFACTURING SYSTEM

Modern industries face critical challenges of wear, corrosion, and short component lifetimes, all of which impose high environmental and economic costs. Sustainable coating solutions are therefore required to enhance durability while reducing waste and energy consumption. Physical Vapor Deposition (PVD) offers an eco-friendly approach, and in recent years high entropy alloys (HEAs) have emerged as promising candidates for protective coatings due to their exceptional mechanical and corrosion-resistant properties. However, limited work has been devoted to understanding the combined influence of substrate temperature and nitrogen incorporation on the microstructure and performance of HEA coatings. In particular, TiVNbMoAl-based coatings and their nitrides (TiVNbMoAl)N have not yet been explored, underscoring the novelty and significance of the present study. This work investigates the synthesis, structure, and properties of TiVNbMoAl high-entropy alloy (HEA) coatings and their nitride counterparts (HEN) deposited by magnetron sputtering. The effect of substrate temperature and nitrogen incorporation on crystallinity, surface morphology, mechanical performance, adhesion, and corrosion behavior was systematically studied, complemented by bulk alloy characterization using mechanical alloying and spark plasma sintering (SPS). XRD confirmed the formation of a stable BCC structure for HEA films and an FCC NaCl-type structure for HEN films. Increasing substrate temperature from room temperature to 400 °C significantly improved crystallinity, reduced lattice strain, and promoted preferred grain orientation. SEM and 3D profilometry revealed that higher deposition temperature produced smoother and denser films, reducing surface roughness by up to about fourfold. Nano indentation (performed under a maximum load of 49.7 mN) showed that HEA hardness increased from 832.62±35.97 HV (RT) to 1130.08±53 HV (400 °C), while HEN hardness more than doubled from 792.22±21.96 HV to 1753.85±39 HV, accompanied by a substantial rise in elastic modulus. Scratch testing confirmed enhanced adhesion at elevated temperature, with HEN coatings showing superior interfacial integrity. Electrochemical studies demonstrated fully active corrosion behavior in NaCl solution; however, HEN-400 °C exhibited the best corrosion resistance due to its dense microstructure and nitride chemistry. Electrochemical impedance spectroscopy (EIS) further reinforced these findings. Nyquist and Bode analyses showed that substrate heating combined with nitrogen incorporation markedly increased charge-transfer resistance and low-frequency impedance, with HEN-400 °C achieving the highest Rct (≈7.6 kΩ·cm²) and the broadest capacitive plateau, indicating the most stable and homogeneous barrier layer. Comparison of all coatings established the corrosion-resistance ranking as HEN-400 °C > HEA-400 °C > HEA-RT > HEN-RT, confirming the strong synergistic role of nitride chemistry and elevated deposition temperature in suppressing electrochemical degradation. Bulk TiVNbMoAl alloy was synthesized via mechanical alloying followed by spark plasma sintering (SPS) to establish a structural and compositional reference for the sputtered coatings. XRD analysis revealed the formation of a stable single-phase BCC solid-solution matrix with minor Al₂O₃ inclusions, confirming the intrinsic phase stability of the TiVNbMoAl system in the bulk state. The SPS-consolidated alloy exhibited a mean Vickers hardness of 810 ± 23 HV under a 5 kgf load, providing a baseline mechanical response of the bulk material. These bulk results demonstrate that the alloy system naturally favors a BCC structure, thereby supporting the interpretation that the FCC NaCl-type structure observed in the nitride coatings originates from nitrogen incorporation and deposition conditions rather than from the inherent alloy chemistry. Overall, nitrogen incorporation combined with substrate heating at 400 °C provided a strong synergistic effect, yielding coatings with superior crystallinity, surface quality, mechanical performance, adhesion, and corrosion resistance. Among all samples, the HEN film deposited at 400 °C demonstrated the most promising balance of properties for advanced protective applications in sustainable manufacturing systems. This research therefore provides new insights into the design of HEA-based nitride coatings, bridging the knowledge gap between deposition parameters and functional performance, and contributing to the development of next-generation protective materials.