Copper becomes unexpectedly hard under extreme strain rate Premium

Massachusetts Institute of Technology and Northwestern University researchers have reported that when pure copper is heated and subjected to an extreme strain rate, it behaves almost like steel.

The discovery of steel transformed the course of human civilisation. The stone age ended with the invention and widespread use of copper smelting and alloying copper with other elements, thus introducing metalworking, new and more durable agricultural implements, the development of culture, trade, and governments, and new weapons of war. When heated, copper turns to liquid, after which it can be moulded into a desired shape. When the mould is cooled, the metal returns to its original solid state, this time in the mould’s shape.

Iron replaced copper and tin in the iron age, but it also did something neither metal could: dissolve carbon. If iron is heated and cooled repeatedly, such that the dissolved carbon is removed until a small amount remains, the powerful iron-carbon alloy known as steel is born. Unlike copper or tin, or even iron, steel is hard — and this made all the difference.

As the economist Yanis Varoufakis wrote in his new book, Technofeudalism: What Killed Capitalism: “The swords of their ironclad enemies sliced through their bronze shields, their ploughs failed to cultivate the less fertile soils, the metal braces holding together their dams and temples were too weak to fulfil the ambitions of forward-thinking architects. In contrast, communities that mustered the techne, the art, of ‘steeling’ iron thrived in the fields, on the battlefields, at sea, in commerce, in the arts.”

If only the people of the bronze age had kept heating copper while straining it greatly, they’d have come across a form of the metal that could rival steel.

A pair of researchers, from the Massachusetts Institute of Technology and Northwestern University, both in the U.S., has reported in a study that when pure copper is heated and also subjected to an extreme strain rate, it behaves like a much harder material would. They attribute this counterintuitive behaviour to new “strengthening mechanisms” that are activated in the material by the higher strain rate. The study was published in the journal Nature on May 22.

“The findings could give rise to new strategies for designing devices to use in extreme conditions like high-speed manufacturing or aerospace engineering, where high temperatures and strain rates are common,” according to a video released by Nature to accompany the paper.

Scientists have already subjected many materials to high strain rates and studied their properties in detail. In the new study, the researchers breached new ground by imparting an even greater strain rate using cutting-edge material-testing technologies.