ICMCTF 2026 Session MA3-3-WeM: High Entropy and Other Multi-principal-element Materials III

Two-dimensional (2D) materials such as graphene and transition metal dichalcogenides (TMDs) exhibit outstanding solid lubrication properties characterized by extremely low coefficients of friction. Their structural and functional properties can be tailored through heterostructure engineering, compositional doping, or controlled introduction of defects. In this work, we introduce a novel class of 2D materials — high-entropy (HE) disulfides — and explore their potential as multifunctional coatings and catalytic materials.

Although HE disulfides remain largely unexplored experimentally, atomistic and thermodynamic simulations predict the stability of several multicomponent compounds. Their synthesis, however, poses significant challenges due to the requirement for high annealing temperatures (~1300 K) and prolonged processing times (~120 hours) under ultrahigh vacuum conditions. Notably, compounds such as (MoWVNbTa)S₂ have demonstrated exceptional electrocatalytic activity for CO₂ conversion, highlighting the promise of this material class.

Our objective is to systematically expand the compositional space of 2D HE disulfides while developing a low-cost, rapid, and scalable deposition approach. To this end, we employ high-throughput atomistic simulations integrated with machine learning and genetic algorithms to identify thermally stable compositions. The most promising candidates are synthesized via high-power impulse magnetron sputtering (HiPIMS) of metallic HE alloy targets in an Ar/H₂S atmosphere, which enables a substantial reduction of processing temperature.

We demonstrate that this approach yields nanocrystalline HE disulfide thin films formed at temperatures below 800 K. Their nano- and macrotribological performance confirms that HE disulfides represent a new and versatile class of 2D materials with strong potential for advanced solid lubrication.

TiZrNbTaMo high entropy alloys (HEAs) with a body-centered cubic (BCC) structure are well known for their excellent compressive yield strength and significant plasticity, which can be retained even in thin film form. These outstanding mechanical properties make them promising candidates for advanced applications. The deposition parameters play a critical role in determining the density, microstructure, and mechanical behavior of HEA thin films. In this study, TiZrNbTaMo high entropy alloy films (HEAFs) were deposited using high power impulse magnetron sputtering (HIPIMS), DC, and RF power sources to investigate the effects of deposition conditions on their structure and properties. HIPIMS, as an advanced physical vapor deposition (PVD) technique, enables a high degree of metal ionization and promotes dense film growth. To further understand plasma effects, the pulse frequency and duty cycle in HIPIMS were systematically varied while maintaining a constant average power. An ion meter was used to evaluate the degree of metal ionization under different peak discharge currents, and pulse-resolved optical emission spectroscopy (OES) was conducted to analyze the temporal evolution of excited species within each HIPIMS pulse, providing insights into discharge behavior and plasma–film interactions. The resulting films were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) to analyze their crystallographic structure and microstructure, while nanoindentation was used to measure hardness and elastic modulus. The TiZrNbTaMo HEAFs deposited by HIPIMS exhibited increased hardness due to the higher peak power density, which induced the coexistence of amorphous and nanocrystalline structures. This study demonstrates that combining HIPIMS deposition with pulse-resolved plasma diagnostics provides an effective approach to control plasma activation and tailor the microstructure and mechanical properties of TiZrNbTaMo high entropy alloy thin films, highlighting their potential for high-performance coating applications.

The design of high-performance structural materials is always pursuing the combination of mutually exclusive properties such as mechanical strength and plasticity. Complex concentrated alloys (CCAs) have recently attracted attention due to their superior mechanical properties, emerging from their multicomponent nature. However, such atomic complexity often prevents a nanoengineering approach with limited control over composition and microstructure, especially in bulk form.

Here, we exploit thin film (TF) synthesis to produce model FCC CCA-TFs with precise control over composition and microstructure (crystalline phase, density of structural defects and grain size), leading to large and tailored mechanical properties. Moreover, our approach encompassed both commonly employed synthesis method (i.e., sputtering) as well as pulsed laser deposition (PLD), leading to the development of novel nanostructures with unique nanoscale features [1].

Firstly, I will demonstrate a simple defect-engineering pathway in sputter-deposited CoCrNi CCA-TFs by introducing Fe to form Fex(CoCrNi)100–x [2]. Increasing the Fe content drives a structural transition from a dual FCC-HCP phase to a single FCC phase, accompanied by a decrease in defect density (stacking faults, nanotwins) and lattice distortion. This results in increased mass density and dislocation mobility, reflected by a decrease in hardness (from 9.6 down to 7.4 GPa), and increment in activation volume (up to ~13 b3).

Then, I will focus on CoCrCuFeNi CCA-TFs by PLD, with unprecedented microstructural control [3]. I will show how to synthetize ultrafine grain structures with controllable size (down to 12 nm) which can be further tailored by post-thermal annealing treatments, resulting in high hardness (11 GPa) and yield strength (2.0 GPa) due to Hall-Petch strengthening, outperforming similar CCA-TFs while maintaining high plasticity (no fracture at 30% strain). Moreover, these ultrafine CCA-TFs show remarkable thermal stability, with grain growth initiating only at 49% of the melting temperature, while maintaining high hardness (9.1 GPa) after annealing for 1h at 460°C.

Overall, we established a comprehensive nanoengineering strategy to tailor structure-property relationships in CCA-TFs, offering new opportunities to overcome the strength-plasticity trade-off.

Among high-entropy alloys, the equiatomic CoCrFeNiMn alloy, commonly known as the Cantor alloy, has emerged as a benchmark system due to its exceptional combination of strength, ductility, and thermal stability, stemming from its single-phase face-centered cubic structure and high-entropy effects. While the bulk properties of CoCrFeNiMn are well established, its behavior in thin-film form remains less explored, particularly under metastable synthesis conditions such as sputter deposition. In this work, we investigate the microstructure, thermal stability, crystal structure, and deformation mechanisms of CoCrFeNiMn thin films synthesized via magnetron sputtering. Films were deposited in an Ar atmosphere using a lab-scale PVD system at different substrate temperatures, with selected samples subjected to post-deposition thermal treatments. X-ray diffraction (XRD) was employed to assess crystal structure and phase formation, while mechanical behavior was probed using nanoindentation, in situ micropillar compression, and micro tensile testing, enabling direct comparison of plasticity and failure modes across multiple loading configurations. Chemical composition was analyzed by energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM) provided insights into grain structure, defect evolution, dislocation activity, and potential deformation twinning. The results reveal the interplay between microstructure and mechanical response in sputtered CoCrFeNiMn thin films, demonstrating how microstructural features and size effects govern strength and ductility. These findings advance the understanding of deformation mechanisms in high-entropy alloys at small scales and inform their potential application as structural materials.

High entropy alloy (HEA) nitride coatings have drawn significant attention owing to their excellent mechanical strength, corrosion resistance, and superior thermal stability. In this study, AlCrNbSiTiNx HEA nitride coatings were deposited on Si wafers, AISI 420, and 304 stainless steel substrates using high power impulse magnetron sputtering (HiPIMS). The effect of nitrogen content on the target poisoning behavior of the equimolar AlCrNbSiTi target was monitored and controlled through a plasma emission monitoring (PEM) feedback control system. Target poisoning ratios ranging from 10% to 90% were systematically examined to evaluate their influence on the microstructure and properties of the coatings. The nitrogen-free AlCrNbSiTi coating exhibited an amorphous structure, while the introduction of nitrogen promoted the formation of a face-centered cubic (FCC) nitride phase. Both the hardness and elastic modulus increased with nitrogen addition due to solid-solution strengthening and the formation of metal nitrides. Thermogravimetric analysis (TGA) conducted at 950 °C in air demonstrated that the AlCrNbSiTiNx coatings possessed excellent oxidation resistance. The relationship between nitrogen content, target poisoning ratio, mechanical properties, and oxidation behavior at 950 °C of the AlCrNbSiTiNx coatings was comprehensively studied in this work.

High power impulse magnetron sputtering (HiPIMS) systems can produce thin films with dense microstructure compared with mid-frequency (MF) sputtering, due to the higher ion energy and plasma density. The combination of MF and HiPIMS has been reported to achieve higher deposition rates and reduced residual stress compared with HiPIMS alone. High entropy alloy (HEA) coatings, composed of multiple principal metallic elements forming carbides, borides, or nitrides, have attracted increasing attention for their exceptional mechanical and chemical stability.

In this study, CrMoNbTiWAg and CrMoNbTiWAgCx HEA carbide coatings were deposited using a superimposed HiPIMS–MF sputtering system. The Ag content was controlled by adjusting the power input to the Ag target, while the acetylene gas flow rate was tuned to control the degree of target poisoning during deposition. Microstructural evolution and phase formation were characterized using FE-SEM, XRD, TEM, and AFM, while mechanical properties such as hardness, adhesion, and wear resistance were evaluated by nanoindentation, scratch, and pin-on-disk tests. Electrochemical and oxidation behaviors were assessed via potentiodynamic polarization in 3.5 wt.% NaCl solution and thermogravimetric analysis (TGA) on X-750 superalloy substrates. Electrical properties were determined through four-point probe measurements, and antibacterial performance was evaluated via bacterial inhibition assays.

This study aims to elucidate the synergistic effects of Ag and C additions in improving the mechanical properties, corrosion protection, and multifunctional durability. The results are expected to provide valuable insights for developing durable and functional HEA carbide coatings through advanced HiPIMS technology.

Keyword: HiPIMS; high entropy alloy carbide; CrMoNbWTiAgCx coating; target poisoning; hardness; corrosion resistance.