ICMCTF 2025 Session MA4-1-TuA: High Entropy and Other Multi-principal-element Materials I

This study unravels the distinct stories of how Cu, Ag, and Au additions transform the structure and properties of CrMnFeCoNi Cantor alloy thin films, revealing behaviors that challenge our initial expectations. Using DC magnetron co-sputtering, we systematically investigated these transformations through comprehensive characterization including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), electrical resistivity measurements, and non-linear optical response.

Each noble metal reveals a unique chapter in phase evolution and property modification, far from the expected systematic progression based on atomic size. Copper tells a story of structural preservation, maintaining the fcc structure while systematically reducing nano-twin density, culminating in near-zero TCR (-2.86 ppm/K) at 37 at% Cu. Silver writes a different narrative through unexpected phase separation, creating artistic patterns of nano-precipitates with a characteristic tweed-like microstructure, despite predictions of solid solution formation. Gold presents perhaps the most surprising tale, where HRTEM unveils large grains with intricate twin boundary networks, contrasting sharply with its apparent amorphous nature in XRD analysis and defying expectations based on atomic size considerations.

The CoCrFeNiMn (Cantor alloy) thin films deposited under ambient and high temperature conditions have been studied from the aspect of microstructure, mechanical, tribological and corrosion properties. The Cantor films were deposited by pulsed direct current magnetron sputtering on silicon wafers at ambient and 350 °C. An FCC phase appeared in both ambient and high temperature films, with small amounts of an unidentified secondary phase. Using nanoindentation, film hardness (H) and reduced elastic modulus (Er) were measured.

Micro-tribology testing was conducted using a 20 μm radius spherical diamond tip in the dry air atmosphere (RH% value under 4.0%), applying normal loads ranging from 2 to 7 mN. The worn surfaces were characterized by atomic force microscopy. Schiffmann’s model was used to evaluate the elastic and plastic components of the friction. The corrosion behaviors of the films were studied by using anodic polarization in 3.5% NaCl, followed by a tribological testing carried out on the corroded surfaces, to address the correlation of corrosion response with the phase composition, mechanical properties and tribological behavior of the films.

Multiple-principal element alloy thin films have attracted lots of interest from academia due to their optimized properties for both functional and structural applications, for example, high strength, good thermal stability, cost efficiency, and lower stacking fault energy. Several previous studies have shown that adding Ti and Al as alloying elements into CoCrNiTiAl multiple-principal element alloy thin films could further enhance their performance. In general, Ti element can transform the face-centered cubic structure into the amorphous structure, while Al generates body-centered cubic (BCC) structures, promoting higher hardness and wear resistance. However, the effect of the addition of Ti and Al elements into CoCrNiTiAl multiple-principal element alloy thin films is still unexplored.

In this work, the CoCrNiTiAl multiple-principal element alloy thin films with different amounts of Ti and Al contents were fabricated by the co-sputtering of TiAl and CoCrNi targets through a hybrid magnetron sputtering system. The CoCrNi and TiAl target were connected with a high power impulse magnetron sputtering system and a radio frequency power supply, respectively. The power input of the TiAl target was adjusted to achieve multiple-principal element alloy thin films with different TiAl contents.The field-emission (FE) scanning electron microscopy, FE-electron probe microanalyzer, X-ray diffraction, nanoindentation, tribometer, and electrochemical workstation were used to characterize microstructure, chemical composition, phase evolution, hardness, wear resistance, and corrosion behavior of multiple-principal element alloy thin films. The effect of TiAl contents on the microstructure and mechanical properties of CoCrNiTiAl multiple-principal element alloy thin films were discussed in this work.

Keywords: multiple-principal element alloy, CoCrNiTiAl, phase transformation, mechanical properties

TiZrNbTaMo high-entropy alloys (HEAs) with a body-centered cubicstructure are known for their excellent compressive yield strength and significant compressive plasticity, retained even in thin film forms. These properties make them promising for various applications.The deposition parameters significantly influence the density and microstructure of thin films, affecting mechanical properties. In this study, TiZrNbTaMo high-entropy alloy films (HEAFs) were prepared using high power impulse magnetron sputtering (HIPIMS), DC, and RF power sources. The effects of pulse frequency and duty cycle in HIPIMS on their structure and properties were systematically investigated.The microstructure and crystal structure of TiZrNbTaMo HEAFs were characterized using transmission electron microscopy (TEM) and X-ray diffractometry (XRD), while their mechanical properties were evaluated by nanoindentation.TiZrNbTaMo HEAFs deposited by HIPIMS exhibited increased hardness due to higher peak power density resulting in the coexistence of amorphous and nanocrystalline structures. However, the highest hardness of 5.78 GPa was achieved with RF power source, which was attributed to more nanocrystalline content and stacking faults.To further improve the mechanical properties of HEAs, post-annealing is used to modify the grain size and structure by inducing microstructures such as stacking faults and twins. In this study, the effects of post-annealing at 900 °C on microstructure and mechanical properties were investigated, and detailed features such as grain sizes, annealing twins, and variations in mechanical properties were discussed.

Hohlraums, centimeter-scale sphero-cylindrical heavy-metal canswith wall thickness of 10 - 100 µm, are a key component of an indirect-drive inertial confinement fusion (ICF) target as it determines the x-ray drive that implodes the fuel capsule. A previous study [Jones et al., Phys. Plasmas 14, 056311 (2007)] has demonstrated the feasibility of improving the x-ray drive by using a hohlraum made from a mixture (“cocktail”) of elements, instead of a single element hohlraums, such as Au or U traditionally used for ICF. Here, we present our results on developing sputter-deposited heavy-metal high-entropy alloys (HEAs) for hohlraums with improved x-ray drive, high electrical resistivity to support a magnetized ICF, and material properties that are compatible with the ICF target fabrication process.

This work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344 and LDRD project 23-ERD-005.