Search Results (6)

High-entropy ceramics (HECs) represent an emerging class of materials composed of at least five different cations or anions in near-equiatomic proportions, garnering significant attention due to their extraordinary functional and structural properties. While multi-component ceramics have played a crucial role for many years, the concept of high-entropy materials was first introduced eighteen years ago with the synthesis of high-entropy alloys, and the first high-entropy nitride films were reported in 2014. These newly developed materials exhibit superior properties over traditional ceramics, such as enhanced thermal stability, hardness, and chemical resistance, making them suitable for a wide range of applications. High-entropy carbides, borides, oxides, oxi-carbides, oxi-borides, and other systems fall within the HEC category, typically occupying unique positions within phase diagrams that lead to novel properties. HECs are particularly well suited for high-temperature coatings, for tribological applications where low thermal conductivity and similar heat coefficients are critical, as well as for energy storage and dielectric uses. Computational tools like CALPHAD streamline the element selection process for designing HECs, while innovative, energy-efficient synthesis methods are being explored for producing dense specimens. This paper provides an in-depth analysis of the current state of the compositional design, the fabrication techniques, and the diverse applications of HECs, emphasizing their transformative potential in various industrial domains. Full article

As protective coatings for the thermal parts of aero-engines, AlCoCrFeNi coatings have good application prospects. In this study, atmospheric plasma spraying (APS) was used to prepare AlCoCrFeNi high-entropy coatings (HECs), which were oxidized from 650 °C to 1000 °C. The mechanism of the oxide layer formation and the internal phase transition were systematically investigated. The results show that a mixed oxide scale with a laminated structure was formed at the initial stage of oxidation. The redistribution of elements and phase transition occurred in the HECs’ matrix; the BCC/B2 structure transformed to Al-Ni ordered B2 phase and Fe-Cr disordered A2 phase. Full article

Multi-component high-entropy (TiCrAl_0.5NbCu)C_xN_y coatings targeting applications requiring medium-to-high friction and wear-resistant surfaces were fabricated through the co-sputtering of elemental targets in an Ar + CH₄ + N₂ reactive atmosphere using a hybrid HiPIMS/DCMS technique. Two sets of samples were fabricated: (a) (TiCrAl_0.5NbCu)C_x high-entropy carbides (HEC) and (b) (TiCrAl_0.5NbCu)C_xN_0.13 high-entropy carbonitrides (HECN), 0 ≤ x ≤ 0.48. The structural, mechanical, tribological, and corrosion resistance properties were thoroughly investigated. The metallic sample exhibits a single BCC structure that changes to FCC via an intermediary amorphous phase through the addition of C or N to the content of the films. The crystallinity of the FCC phases is enhanced and the density of the films decreases down to 5.5 g/cm³ through increasing the carbon fraction up to 48%. The highest hardness of about 16.9 GPa and the lowest wear rate of about 5.5 × 10⁻⁶ mm³/Nm are presented by the samples with the largest carbon content, x = 0.48. We found a very good agreement between the evolution of H/E and H³/E² parameters with carbon content and the tribological behavior of the coatings. The best corrosion resistance was presented by the low-carbon carbonitride samples, showing a charge transfer resistivity of about 3 × 10⁸ Ω∙cm, which is more than three times larger than that of the metallic HEA. The best tribological characteristics for envisioned application were presented by (TiCrAl_0.5NbCu)C_0.3N_0.13, showing a coefficient of friction of 0.43 and a wear rate of about 7.7 × 10⁻⁶ mm³/Nm. Full article

Surface coatings that operate effectively at elevated temperatures provide compatibility with critical service conditions as well as improved tribological performance of the components. High-entropy coatings (HECs), including metallic, ceramics, and composites, have gained attention all over the world and developed rapidly over the past 18 years, due to their excellent mechanical and tribological properties. High-entropy alloys (HEAs) are defined as alloys containing five or more principal elements in equal or close to equal atomic percentage. Owing to the high configurational entropy compared to conventional alloys, HEAs are usually composed of a simple solid solution phase, such as the BCC and FCC phases, instead of complex, brittle intermetallic phases. Several researchers have investigated the mechanical, oxidation, corrosion and wear properties of high-entropy oxides, carbides, borides, and silicates using various coating and testing techniques. More recently, the friction and wear characteristics of high-entropy coatings (HECs) have gained interest within various industrial sectors, mainly due to their favourable mechanical and tribological properties at high temperatures. In this review article, the authors identified the research studies and developments in high-entropy coatings (HECs) fabricated on various substrate materials using different synthesis methods. In addition, the current understanding of the HECs characteristics is critically reviewed, including the fabrication routes of targets/feedstock, synthesis methods utilized in various research studies, microstructural and tribological behaviour from room temperature to high temperatures. Full article

High-entropy materials (HEM), including alloys, ceramics, and composites, are a novel class of materials that have gained enormous attention over the past two decades. These multi-component novel materials with unique structures always have exceptionally good mechanical properties and phase stability at all temperatures. Of particular interest for high-temperature applications, e.g., in the aerospace and nuclear sectors, is the new concept of high-entropy coatings (HEC) on low-cost metallic substrates, which has just emerged during the last few years. This exciting new virgin field awaits exploration by materials scientists and surface engineers who are often equipped with high-performance computational modelling tools, high-throughput coating deposition technologies and advanced materials testing/characterisation methods, all of which have greatly shortened the development cycle of a new coating from years to months/days. This review article reflects on research progress in the development and application of HEC focusing on high-temperature applications in the context of materials/composition type, coating process selection and desired functional properties. The importance of alloying addition is highlighted, resulting in suppressing oxidation as well as improving corrosion and diffusion resistance in a variety of coating types deposited via common deposition processes. This review provides an overview of this hot topic, highlighting the research challenges, identifying gaps, and suggesting future research activity for high temperature applications. Full article

Cavitation corrosion resistant coatings are an excellent solution to the cavitation corrosion problem. High entropy alloys provide a new possibility for cavitation resistant coatings due to their excellent comprehensive performance. Laser cladding was employed to synthesize AlCoCr_xCuFe (x represents the Cr concentration, x = 0.5, 1.0, 1.5, 2.0) high entropy alloy coatings (HECs) on AISI 304 steel. The phase transformation, microstructure, micro-mechanical properties, and cavitation erosion performance of HECs were studied. Results showed that AlCoCr_xCuFe HECs were composed of BCC and FCC duplex phase. The microstructure of HECs showed a typical dendritic structure. The composition segregation of interdendrite structures was observed. Cavitation erosion resistance represented by 20 h volume loss was decreased with the increase in Cr content. AlCoCr_xCuFe HECs with the lowest chromium content (AlCoCr_0.5CuFe) showed the best cavitation erosion resistance among all samples. The cavitation resistance of AlCoCr_xCuFe HECs has good correlation with the mechanical parameter $H_{\mathrm{n}}{}^3$/$E_{\mathrm{r}}{}^2$($H_{\mathrm{n}}$ is nanohardness, $E_{\mathrm{r}}$ is elastic modulus) and phase formation parameter δ (δ is atomic radius difference). The surface after 20 h of cavitation erosion testing exposed the dendritic structure of BCC phase, which was caused by the destruction of the interdendrite structure by cavitation impact. Full article