Lehigh University Ceramics Researchers Shed Light On Metal Embrittlement

Why does a solid metal that is engineered for ductility become brittle, often suddenly and with dramatic consequences, in the presence of certain liquid metal impurities? The phenomenon, known as liquid metal embrittlement, or LME, has baffled metallurgists for a century. Now, a team of ceramics researchers has shed light on LME by obtaining atomic-scale images of unprecedented resolution of the grain boundaries, or internal interfaces, where LME occurs.

In doing so, says Martin Harmer, professor of materials science and engineering at Lehigh University, the researchers have achieved the first direct observation in a metal system of a bilayer grain boundary phase transition.

The study suggests that interior interfaces can undergo transitions similar to the solid-to-liquid and liquid-to-gas phase transitions that occur in larger, "bulk" materials.

It also paves the way for scientists to prevent LME by strengthening the chemical bonds of the materials present at grain boundaries.

"This is a very exciting discovery," says Harmer, who directs Lehigh's Center for Advanced Materials and Nanotechnology. "It gives us a much clearer understanding of the atomic mechanism of LME and it promises to improve our ability to control and fine-tune the properties of metals and other materials during fabrication."

Harmer and his colleagues reported their findings Sept. 23 in Science magazine.

Their 18-month study was funded by the U.S. Navy. The group will continue its work, with a focus on rectifying LME-related problems in metals, with help from a five-year, $7.5 million grant through the Department of Defense's Multidisciplinary University Research Initiative program. That project involves researchers from Lehigh, Carnegie-Mellon, Clemson, Illinois and Kutztown universities.