Steel breaks record for not breaking

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The new steel alloy is so resilient that it bounces back into shape, even when hit with cannon-fired projectiles(Credit: UC San Diego)

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With iron being one of the most abundant metals on Earth, its transformation into steel also makes it one of the most useful. With applications in almost every realm of manufacturing and construction technology, steel has been the material on which the very structure of modern society has been built. In recent years, though, the heavy and unwieldy nature of steel has seen its decline as lighter – but more brittle – alloys replace it. Now a team of engineers has created a steel alloy that should be cheaper to produce than competing alloys, while being exceptionally strong without being brittle. The researchers believe that the new steel alloy could be incorporated in everything from motor vehicles and spacecraft to tools and armor.

A multidisciplinary team from the University of California at San Diego (UC SanDiego), the University of Southern California (USC) and the California Institute of Technology (CIT), has created a new amorphous metal dubbed SAM2X5-630 by using metallic glass matrix composites (MGMC) to replace a number of atoms in standard steel's crystal-like structure. In effect, this amalgam of materials creates a new version of steel that has incredible resilience to shock, and is able to bounce back into shape, rather than bend or tear as ordinary steel can do under high-pressure.

In fact, according to the researchers, the new steel alloy can stand up to pressures of over 12.5 giga-Pascals (more than 1.8 million psi, or about 125,000 atmospheres) without being permanently deformed.This is the highest recorded elastic limit for any steel alloy. Engineers at USC tested the alloy by bombarding samples of the material with 34 mm (1.3 in) copper plates fired from a naval powder gun at 500 to 1,300 m/s (1,640 - 4,265 fps). The material deformed slightly on initial impact, but bounced back immediately afterwards.

"The fact that the new materials performed so well under shock loading was very encouraging and should lead to plenty of future research opportunities," said Professor Veronica Eliasson from the Department of Aerospace and Mechanical Engineering at USC.

The search for increasingly versatile alloys of steel is driven not only by iron's abundance and low cost, but by the fact that steel is an exceptionally hard-wearing metal that also makes a range of exceptionally useful alloys when mixed with other materials. Notable in these is the creation of tool steel with the addition of vanadium, the making of stainless steel by adding chromium, and even versions using aluminum and nickel that make steel as light and strong as titanium.

In the case of SAM2X5-630, the addition of MGMC with the mixed metal powders helped achieve exceptional hardness in the material when heated. To create the solid metal, a process called spark plasma sintering was used, where the powders were placed in a graphite mold then pressurized to 100 mega-Pascals (around 1,000 atmospheres or about 14,500 psi), and heated to a temperature of some 1,165° F (630° C) while an electric current of more than 10,000 amps was run through it. According to the researchers, this technique provides very large time and energy savings.

"You can produce materials that normally take hours in an industrial setting in just a few minutes," said Professor Olivia Graeve from the Jacobs School of Engineering at UC San Diego. "Because these materials are designed to withstand extreme conditions, you can process them under extreme conditions successfully."

With continuing research aiming to make the materials even more resistant to impacts, the team believes that the the resilience of its new alloy would make it ideal for esoteric uses like satellite casings that protect from high-speed micrometeorite impacts, as well as military applications in making armor that would simply bounce back when hit, or even in everyday situations in creating drill bits that don't snap as easily as traditional ones.

The results of this research were recently published in the journal Nature.

The short video below shows the new steel being subjected to drop tests in the laboratory.

Source: UC San Diego

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