Alloys, which are materials such as steel that are made by combining two or more metallic elements, are among the underpinnings of contemporary life. They are essential for buildings, transportation, appliances and tools—including, very likely, the device you are using to read this story. In applying alloys, engineers have faced an age-old trade-off common in most materials: Alloys that are hard tend to be brittle and break under strain, while those that are flexible under strain tend to dent easily.
Now, a UCLA-led research team has provided an unprecedented view of the structure and characteristics of medium- and high-entropy alloys. Using an advanced imaging technique, the team mapped, for the first time ever, the three-dimensional atomic coordinates of such alloys. In another scientific first for any material, the researchers correlated the mixture of elements with structural defects. The study was published Dec. 20 in the journal Nature.
“Medium- and high-entropy alloys had been previously imaged at the atomic scale in 2D projections, but this study represents the first time that their 3D atomic order has been directly observed,” said corresponding author Jianwei “John” Miao, a professor of physics in the UCLA College and member of the California NanoSystems Institute at UCLA. “We found a new knob that can be turned to boost alloys’ toughness and flexibility.”
Medium-entropy alloys combine three or four metals in roughly equal amounts; high-entropy alloys combine five or more in the same way. In contrast, conventional alloys are mostly one metal with others intermixed in lower proportions. (Stainless steel, for example, can be three-quarters or more of iron.)
To understand the scientists’ findings, think of a blacksmith forging a sword. That work is guided by the counter-intuitive fact that small structural defects actually make metals and alloys tougher. As the blacksmith repeatedly heats a soft, flexible metal bar until it glows and then quenches it in water, structural defects accrue that help turn the bar into an unyielding sword.
2023-12-20 22:00:04
Link from phys.org rnrn