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.

In this paper, an investigation of the load-dependent wear behavior of copper-free semi-metallic brake material is presented. The experiments were conducted in ambient thermal settings with varying sliding velocities (3.141 m/s, 2.09 m/s, and 1.047 m/s), normal load (60 N, 50 N, and 40 N), and sliding distance (4500 m, 3000 m, and 1500 m). Taguchi’s method was used in designing experiments to examine the output through an L9 orthogonal array. ANOVA was used to identify the consequence of interactions among different constraints. It also established the significant contribution of each process factor. The objective was set as the ‘smaller is better’ criterion to find minimum wear conditions. The impact of the normal load on the wear process was found to be maximum (71.02%), followed by sliding velocity (27.84%) and sliding distance (1.14%). The optimum condition for the minimum wear rate was found at 40 N normal load, 1500 m sliding distance, and 3.14 m/s sliding velocity. The results were confirmed with validatory friction experiment runs. The resulting error was within 10% error, which verified the experiment methods. The SEM investigation of worn surfaces of pin and disc confirmed abrasive wear and adhesive wear at 60 N and 40 N, respectively.

The transportation sector contributes to urban particulate matter (PM) pollution through emissions from both exhaust and non-exhaust processes. Among non-exhaust sources, brake wear debris from automotive brake pad-disc systems is a significant yet often underestimated pollutant. Brake wear emissions consist of airborne particles that disperse into the atmosphere and non-airborne particles that deposit on vehicle surfaces, roadways, and surrounding infrastructure. Airborne particles worsen urban air quality issues, while non-airborne debris can be resuspended due to traffic or environmental factors, contributing to waterway contamination through surface runoff. Brake wear generates particles ranging from nanometers to micrometers, with a substantial fraction falling in the fine particulate range, posing critical health risks. This review synthesizes current knowledge on the mechanisms of brake wear particle generation, the physicochemical characteristics of the emitted debris, and its environmental dispersion and health implications. It also explores how material properties and operational conditions influence particle formation. By addressing the challenges associated with brake wear emissions, this study emphasizes the need for advanced materials and innovative design strategies to mitigate their environmental and health impacts.