Discover the remarkable process of work hardening, where deformation transforms soft materials into astonishingly strong ones. Researchers have unveiled the underlying mechanisms behind this universal phenomenon, shedding light on the future of material design and manufacturing.
From Bronze Age to Modern Day
The secret of work hardening was first discovered 4,000 years ago by the earliest smiths of the Bronze and Iron Ages. They discovered metal became stronger when they had simply bent it or hammered it. Actually, this work or strain hardening process is still used today in metallurgy and manufacturing for a variety of items, from car frames to power lines.
But despite how useful migration can be, materials scientists have never been able to see the phenomenon occurring in real-time — until now. Recently, a group of researchers from Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), recorded the detailed mechanisms responsible for work hardening — work that has challenged scientists in the field for more than half-century. The cutting-edge research was carried out at the Harvard Materials Research Science and Engineering Center (MRSEC) and helps us better understand the strength of materials, ultimately allowing us to design and fabricate completely new materials in a revolutionary way.
Unveiling the Secrets of Work Hardening
For more than a half-century, work hardening has perplexed materials scientists because the atomic structures that are responsible for it can only be seen using an electron microscope. While researchers could compare the before and after structure of a material — how it deforms, say, before a car crashes into it and shatters or during mixing pyrite or silver nanoparticles with liquid chemicals called ionic liquids to develop liquid crystals — they couldn’t see what was happening during that transformation.
Studies have shown that the secret to work hardening is dislocations, imperfections in a material´ s structure. These defects eventually form a network that results in the material becoming stronger. Nonetheless, the specific types of defect microscopic interactions and their distinct impact on the hardening process remain elusive.
Looking to get a more detailed picture of this, researchers from the study sought an unlikely source: colloidal crystals. These particles are ∼10000 times larger than atoms, but share similar crystalline geometries1,2, phase behaviour and defects as atoms. The key advantage? These colloidal crystals are extremely pliable, allowing researchers to detect the movement of every single particle under a confocal optical microscope – something that you would never be able to do with your typical metal sample.
Conclusion
This work establishes the operational principles driving this essential process, which are understood to govern all such transformations by any means. According to the researchers, by studying how those soft materials behave and transmogrify into useful yet hard structures, they have made ‘important discoveries that will inform new design and fabrication strategies’ in the field of material science. Image: The Readily Observable Spatiotemporal Arrangement of Defects and Dislocations In Situ (ROSAKU) approach uses a special high-rate camera that can capture over 100 million frames per second, fast enough to view the dynamic evolution of material strength properties in real time.
