ADVANCED MATERIALS & PROCESSES | JANUARY/FEBRUARY 2025 25 For many centuries during the Copper, Bronze, and Iron Ages, traditional alloy systems primarily focused on incorporating additional elements into a matrix dominated by one dominant element and forming a solid solution. High-entropy alloys (HEAs) represent a new class of materials that have garnered significant attention in the field of materials science. Unlike traditional alloys, HEAs are formed by mixing five or more elements in roughly equal proportions (Fig. 1). Initially, it was thought that using multiple principal elements would result in complex and unstable microstructures, which limited early research interest. However, recent findings show that HEAs made up of elements with strong chemical compatibility can form a limited number of solid solution phases, and in some cases just one. This behavior is due to their high mixing entropy. This special class of materials is known by various names including high-entropy alloys, multi-principal element alloys, and multicomponent alloys[1]. UNLOCKING THE POTENTIAL OF HIGH-ENTROPY ALLOYS WITH ADVANCED CHARACTERIZATION TECHNIQUES As high-entropy alloys become more complex in terms of microstructure, phase stability, and intermetallics, the advent of sophisticated analytical instruments is helping scientists to develop new materials with the most desirable properties. Raja Gopala Chary Thipparthi and R.J. Immanuel* Indian Institute of Technology Bhilai, Durg, India *Member of ASM International while XRD is useful for nondestructively identifying crystal structures, phases, and lattice parameters. SEM resolution is surpassed by TEM resolution, enabling atomic-level viewing of materials. These methods work well together to provide comprehensive knowledge of characteristics such as defects, phase composition, crystallinity, and grain size. As materials become more complex in terms of microstructure, phase stability, and intermetallics, Due to their complex structure, it is imperative to use advanced tools to better understand these materials. Conventional techniques such as scanning/transmission electron micro- scopy (S/TEM) and x-ray diffraction (XRD) are helpful for analyzing the composition, phase structure, and other properties of HEAs. Electron microscopes help reveal fine grain structures at high resolution along with performing elemental distribution and mapping, (a) (b) Fig. 1 — (a) A bcc alloy with the lattice made of primary element atoms ‘A’ with a substitutional solute atom ‘B;’ and (b) a bcc high-entropy alloy with five different elements, A, B, C, D, and E, taking the lattice positions.
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