Since the Iron Age, metallurgists have known that metals such as steel become stronger and harder the more you hit (or beat) on them.
But it wasn't always clear why this happened. Vasily Bulatov and colleagues at Lawrence Livermore National Laboratory discovered that the common explanation for this hardening process ignored a key component.
Through a series of computer simulations and experiments using the metal molybdenum, the team determined that three line defects (also known as dislocations) in the crystal structure of metals create a stronger bond than when only two dislocations intersect. Dislocations are the displacements of the regularly packed layers of atoms within the crystal structure.
The theory of dislocation was invented in the 1930s. Research since then has focused on dislocation interactions and their role in hardening metals, in which continued deformation increases the metal’s strength (much like a blacksmith pounding on steel with an anvil).
But the Livermore team found that three or more dislocations create a strong, nearly indestructible locking mechanism. “When you beat on metal, dislocations multiply like crazy,” Bulatov said. “The metal gets stronger, but we didn't know exactly how that strength came about. What we found was that the strength becomes greater each time three dislocation lines intersect.”
Bulatov said the hardening mechanism could be applied in any strong metal, from bridges to ships to rebar within the walls of buildings.
Potentially, you can take advantage of this behavior,” he said. “Dislocation interaction was known for 70 years. We now show exactly how it happens. Two at the time was thought to do it, but three at a time makes a big difference.”
The research appears in the April 27 edition of the journal Nature. Other Livermore researchers include Luke Hsiung, Meijie Tang, Athanasios Arsenlis, Maria Bartelt, Wei Cai, Jeff Florando, Masato Hiratani, Moon Rhee, Gregg Hommes, Tim Pierce and Tomas Diaz de la Rubia.
Source: Lawrence Livermore National Laboratory
Related stories:
Metal deformation studies lead to new understanding of materials at extreme conditions
Researchers have found a new tool to explore materials at extreme conditions. By combining very large-scale molecular dynamics simulations with time-resolved data from laser experiments of shock wave propagation through specific metals, scientists at the Lawrence Livermore National Laboratory are now able to better understand the evolution of high-strain-rate plasticity.
Spiraling nanotrees offer new twist on growth of nanowires
Since scientists first learned to make nanowires, the nano-sized wires just a few millionths of a centimeter thick have taken many forms, including nanobelts, nanocoils and nanoflowers.
Smaller is stronger -- now scientists know why
As structures made of metal get smaller -- as their dimensions approach the micrometer scale (millionths of a meter) or less -- they get stronger. Scientists discovered this phenomenon 50 years ago while measuring the strength of tin "whiskers" a few micrometers in diameter and a few millimeters in length. Many theories have been proposed to explain why smaller is stronger, but only recently has it become possible to see and record what's actually happening in tiny structures under stress.
Platinum nanocrystals boost catalytic activity for fuel oxidation, hydrogen production
A research team composed of electrochemists and materials scientists from two continents has produced a new form of the industrially-important metal platinum: 24-facet nanocrystals whose catalytic activity per unit area can be as much as four times higher than existing commercial platinum catalysts.
Model simulates atomic processes in nanomaterials
Researchers from MIT, Georgia Institute of Technology and Ohio State University have developed a new computer modeling approach to study how materials behave under stress at the atomic level, offering insights that could help engineers design materials with an ideal balance between strength and resistance to failure.
Researchers gain new insight into strength of crystalline industrial materials
A team of 11 researchers, including 10 at Lawrence Livermore National Laboratory and one at Stanford University, has gained a fundamental new insight into the physical strength of crystalline materials, which perhaps surprisingly include the industrial mainstays of aluminum, iron, gold and silicon. Findings of the study, which was led by Lawrence Livermore researcher Vasily V. Bulatov, appear in the April 27 issue of the journal
Nature.
Scientists fashion semiconductors into flexible membranes
University of Wisconsin-Madison researchers have demonstrated a way to release thin membranes of semiconductors from a substrate and transfer them to new surfaces-an advance that could unite the properties of silicon and many other materials, including diamond, metal and even plastic.
Breakthrough in Nanoscale Understanding of Metal Shape Change
A
nanocrystalline metal is one whose average grain size is measured in billionths of a meter, much smaller than in most ordinary metals. As the grain size of a metal shrinks, it can become many times stronger, but it also usually loses ductility. To take advantage of increasing strength with decreasing grain size, researchers must first understand a fundamental problem:
by what processes do nanosized crystals of metal stretch, bend, or otherwise deform under strain?
