Researchers at Yale University and the Texas Tech University have found a way of predicting whether a given glass will be ductile or brittle.
A glass sculpture called ‘The Sun’ at the Gardens of Glass exhibition in Kew Gardens, London, made from 1,000 separate glass objects by Dale Chihuly (Adrian Pingstone)
“Most of us think of glasses as brittle, but our finding shows that any glass can be made ductile or brittle,” said Prof Jan Schroers, senior author of a study appearing in the journal Nature Communications.
“We identified a special temperature that tells you whether you form a ductile or brittle glass,” he said.
Ductility refers to a material’s plasticity, or its ability to change shape without breaking. The key to forming a ductile glass is cooling it fast. Exactly how fast depends on the nature of the specific glass.
Focusing on a new group of glasses known as bulk metallic glasses (BMGs) – metal alloys, or blends, that can be extremely pliable yet also as strong as steel – researchers studied the effect of a so-called critical fictive temperature (CFT) on the glasses’ mechanical properties at room temperature.
When forming from liquid, there is a temperature at which glass becomes too viscous for reconfiguration and freezes. This temperature is called the glass transition temperature. Based on experiments with three representative bulk metallic glasses, the researchers said there is also, for each distinct alloy, a critical temperature that determines the brittleness or plasticity of the glass.
“It’s possible to categorize glasses in two groups – those that will be brittle because in liquid form their CFT is above the glass transition temperature, and those that will be ductile, because in liquid form their CFT is below the glass transition temperature.”
They previously thought a liquid’s chemical composition alone would determine whether a glass would be brittle or ductile.
“That’s not the case,” Prof Schroers said. “We can make any glass theoretically ductile or brittle. And it is the critical fictive temperature which determines how experimentally difficult it is to make a ductile glass. That is the major contribution of this work.”
“The finding applies theoretically to all glasses, not metallic glasses only.”
“A glass can have completely different properties depending on the rate at which you cool it,” Prof Schroers said. “If you cool it fast, it is very ductile, and if you cool it slow it¹s very brittle. We anticipate that our finding will contribute to the design of ductile glasses, and in general contribute to a deeper understanding of glass formation.”
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Bibliographic information: Golden Kumar et al. 2013. Critical fictive temperature for plasticity in metallic glasses. Nature Communications 4, article number: 1536; doi: 10.1038/ncomms2546
