Researchers have demonstrated a technique that allows them to track microscopic changes

 in metals or other materials in real time even when the materials are exposed to extreme heat 

and loads for an extended period of time—a phenomenon known as "creep." The technique 

will expedite efforts to develop and characterize materials for use in extreme environments, 

such as nuclear reactors.

"Until now, you could look at a material's structure before exposing it to heat or load, then 

apply heat and load until it broke, followed by a microstructural observation. That means you'd 

only know what it looked like before and after loading and heating," says Afsaneh Rabiei, 

corresponding author of a paper on the work and a professor of mechanical and aerospace 

engineering at North Carolina State University.

"Our teand its behavior under different conditions of loading and heating."

Rabiei developed the in situ SEM technique for high temperatures and load (tension) as a 

means of conducting high throughput assessments of the behavior of advanced materials. The 

goal was to be able to predict how a material responds under a variety of heating and loading 

conditions. The project was supported by the Department of Energy. The instrument can 

capture SEM images at temperatures as high as 1,000 degrees Celsius (C), and at stresses as 

high as two gigapascal—which is equivalent to 290,075 pounds per square inch.

For their recent demonstration of the technique's potential, researchers conducted "creep-

fatigue" testing on a stainless steel alloy called alloy 709, which is being considered for use in 

nuclear reactors.

"Creep-fatigue testing involves exposing materials to high heat and repeated, extended loads, 

which helps us understand how structures will perform when placed under loads in extreme 

environments," Rabiei says. "That is clearly important for applications such as nuclear 

reactors, which are designed to operate for decades."chnique, which is called 'in situ scanning 

electron microscopy (SEM) heating and loading,' allows us to see the microscopic changes 

taking  place  throughout  the process.  You  can  see  how  cracks  form  an d grow,  or  how 

microstructure  transforms  during  the  failure process.  This  is  extremely  valuable for 

understanding a material's characteristics