Discover Top Posts Tagged with #grain boundaries

How defects make permanent magnets even more efficient

Rare-earth magnets are essential for electric motors in vehicles, drones, and trains, forming the backbone of modern, environmentally friendly mobility. These are not simple blocks of metal, but carefully engineered materials with a complex internal nanostructure composed of tiny building blocks called phases, each with its own crystal structure, chemistry, and physical properties. How magnetization behaves at the interfaces between these tiny building blocks and how well it resists demagnetizing forces ultimately determines the strength and stability of the magnet, and therefore the efficiency and reliability of the motor or generator. By combining advanced magnetic measurements, various microscopy techniques, and micromagnetic simulations, researchers from the DFG Collaborative Research Center investigated a high-performance samarium-cobalt magnet, Sm2(Co,Fe,Cu,Zr)17, which is known for its excellent thermal and chemical stability. Atomic-scale imaging revealed that while high- and medium-performance magnets can appear structurally similar, they differ substantially in their chemical composition at the nanoscale. The research is published in Nature Communications.

Simulations show why grains in metals and ceramics grow the way they do

A team of international scientists headed by Prof. Marco Salvalaglio from TUD–Dresden University of Technology has found out that internal stresses—not just interface energy—play a key role in shaping the microstructure of crystalline materials. These findings challenge classical theories and could improve how we design materials for engineering and technology. The results have recently been published in the Proceedings of the National Academy of Sciences. Polycrystalline materials are made up of many tiny crystals called grains and are found everywhere, from rocks in nature to metals and ceramics in engineering. The way these grains are arranged and how they change over time has a big impact on important properties like strength, flexibility, and electrical conductivity. Understanding what drives these changes, especially the role of internal stresses inside the material, is key to explaining how materials behave and to designing better ones for specific uses.

Allowing atoms to come and go can open the door to better materials modeling

Most materials, especially metals and ceramics, are crystals. Their atoms are arranged in three-dimensional lattices that repeat the same exact pattern, over and over again. But there's a well-known saying in materials science: "Crystals are like people. It is the defects that tend to make them interesting." New model tackles crystal defects In a new study, published in Physical Review Letters, researchers from Lawrence Livermore National Laboratory (LLNL) created a new model for crystal defects at realistic temperatures. The simulation technique overcomes long-standing challenges in the field to calculate material structure and properties that were previously impossible to obtain. The result points the way toward improved production and performance of materials.

New insights into grain boundary kinetics challenge traditional views

Researchers from City University of Hong Kong (CityUHK), in collaboration with experts from local and overseas universities, have reshaped scientists' fundamental understanding of the kinetic processes in crystalline materials, throwing light on new approaches for materials processing and microstructure tailoring. This research is published in Science, titled "Grain boundaries are Brownian ratchets." Crystals are characterized by well-arranged atoms in a lattice structure. Grain boundaries are planar defects where crystals with different orientations meet. Most crystalline materials are polycrystals, aggregates of many polyhedral crystallite grains with different orientations.

Alloy design model offers faster, more accurate predictions by factoring in material defects

Humans began creating alloys about 5,000 years ago by combining copper and tin to produce bronze. Since then, alloy design has advanced dramatically, says Moneesh Upmanyu, professor of mechanical and industrial engineering at Northeastern University. "Now, it's definitely a science [and] less of an art because we have the periodic table and we know the properties of all these elements that we are mixing together," he says. The Journal of Applied Physics recently selected Upmanyu's new research paper on alloy design as an Editor's Pick. The paper introduces a new computational model that offers strategies for alloy design of real materials in seconds. Compared to traditional lab experiments and AI-based approaches, the model offers greater speed, cost efficiency and accuracy.

The corners where atoms meet may provide a path to new materials for extreme conditions

How can we engineer materials that are stronger and lighter? What about new materials for extreme conditions, such as in jet engines and spacecraft? The answer, says Fadi Abdeljawad, an associate professor of materials science and engineering in Lehigh University's P.C. Rossin College of Engineering and Applied Science, might be hidden in the infinitesimally tiny regions, or boundaries, where atoms in crystals come together. Along with his collaborators at the U.S. Department of Energy's Center for Integrated Nanotechnologies (CINT), Abdeljawad is uncovering how those tiny boundaries have such an enormous impact on the characteristics of nanomaterials. "Atoms come together to form nanocrystals, which are essentially structures about 1/10,000th the width of a human hair," explains Abdeljawad. "Think of these crystals coming together like pieces of a puzzle, or as tiles on a kitchen floor. Billions of these nanocrystals stack on top of each other to form most engineering materials."

An effective strategy to inhibit grain coarsening: Construction of multi-element co-segregated grain boundary complexion

To date, ceramic scientists have devised various strategies to impede grain coarsening. The utilization of nano-sized precursor powder can not only facilitate the densification process, but also yields bulk ceramics with reduced grain sizes compared with micron-sized precursor powder. Rapid sintering bypasses the low-temperature surface diffusion stage and directly enters the high-temperature sintering stage through rapid heating, rendering it an effective way to inhibit grain coarsening. However, these aforementioned strategies fail to prevent coarsening during the application of nano-ceramics in medium- or high-temperature environments. The introduction of the secondary phase can also enhance thermal stability of nanograins. By pinning grain boundaries (GBs) and reducing their mobility, the secondary phase effectively inhibits coarsening. However, it is challenging to achieve a uniform distribution of the secondary phase, which may cause detrimental effects on other properties.

Watching Defects Melt in a Crystal

Researchers have experimentally captured the melting of defects in a crystal, a process previously only understood through simulations. [...] Theorists predict that the melting of a crystalline solid happens in three stages. First, a liquid film forms on the surface. Second, defects between neighboring crystallites fluidize, causing the crystal to lose its rigidity. And third, the remaining solid parts liquefy. Researchers have observed the first and third stages of this melting process but not, until now, the second. By measuring how laser light scatters off heated crystalline tin samples, Emil Polturak and Steve Lipson of Technion–Israel Institute of Technology have detected changes in the samples’ shape that they show correspond to the melting of defects known as grain boundaries [1]. The study provides an optical tool for examining melting stages in metallic crystals.

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