A stainless steel alloy — alloy 709 — has potential for elevated-temperature applications such as nuclear reactor structures. It is exceptionally strong and resistant to damage when exposed to high temperatures for long periods of time, making it a promising material for use in next-generation nuclear power plants.
In order to demonstrate the material's capabilities, a new technique was developed that performs scanning electron microscopy (SEM) in real time while applying extremely high heat and high loads to a material.
This enables researchers to see the crack growth, damage nucleation, and microstructural changes in the material during thermomechanical testing that are relevant to any host material. The technique can help in understanding where and why materials fail under a wide variety of conditions — from room temperature up to 1000 °C (1832 °F), and with stresses ranging from 0 to 2 gigapascal (290,075 pounds per square inch).
The researchers exposed one-millimeter-thick samples of alloy 709 to temperatures as high as 950 °C until the material “failed,” meaning the material broke. Alloy 709 outperformed 316 stainless steel, which is the material currently used in nuclear reactors. The study shows that alloy 709's strength was higher than that of 316 stainless steel at all temperatures, meaning it could bear more stress before failing; for example, alloy 709 could handle as much stress at 950 °C as 316 stainless steel could handle at 538 °C.
The microscopy technique enabled researchers to monitor void nucleation and crack growth along with all changes in the microstructure of the material throughout the entire process. The next step is to assess how alloy 709 will perform at high temperatures when exposed to cyclical loading or repeated stress.