Forming metal into the specific shapes needed for various purposes is done in many ways, including casting, machining, forging, and rolling. These processes affect the sizes and shapes of the tiny crystalline grains that make up the bulk metal, whether it be steel, aluminum, titanium, or other widely used metals and alloys.
Researchers at MIT have now been able to analyze exactly what happens as these crystal grains form during an extreme deformation process, at the tiniest scales, down to a few nanometers across. The new discoveries could lead to improved ways of processing to produce better, more consistent properties such as hardness and toughness.
The new findings, made possible by detailed analysis of images from a suite of powerful imaging systems, are reported today in the journal Nature Materials, in a paper by former MIT postdoc Ahmed Tiamiyu (now assistant professor at the University of Calgary); MIT professors Christopher Schuh, Keith Nelson, and James LeBeau; former student Edward Pang; and current student Xi Chen.
“In the process of making a metal, you are endowing it with a certain structure, and that structure will dictate its properties in service,” Schuh says. In general, the smaller the grain size, the stronger the resulting metal. Striving to improve strength and toughness by making the grain sizes smaller “has been an overarching theme in all of metallurgy, in all metals, for the past 80 years,” he says.
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