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Manufacturing Technology Insights | Friday, June 21, 2024
Certain industrial materials are expected to retain their performance and qualities even in the most extreme conditions. When used in space exploration, cryogenic storage tanks, and ice-breaking equipment, these materials need to maintain impact toughness and tensile strength while also being resistant to the effects of low temperatures.
Fremont, CA: At low temperatures, most metals and materials become more brittle. This happens because at cryogenic temperatures, the movement of atoms in the crystal lattice is restricted, which means that there are no 'slip systems' to allow for distortions. With limited mobility, cracks are more likely to form, making the material brittle.
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However, not all materials are equally sensitive to temperature and macroscopic behavior. Some cryogenic materials, such as aluminum, titanium, and certain steel alloys, offer potential alternatives.
The growing interest in a 'hydrogen economy,' where hydrogen replaces many fossil fuels as the preferred energy source, is spurring the development of new cryogenic materials for liquid helium storage. But there is a challenge in developing experimental methods to measure brittle behavior at the atomic level and identify materials likely to have toughness at cryogenic temperatures.
Characterizing cracks and defects requires high spatial resolution and 3D reconstruction capabilities. It is also important to use X-rays with good penetration depth to assess both the bulk of the material and the surface, which will help expand our understanding of the challenges posed by cryogenic materials.
This article explores the experimental techniques used to characterize brittle behavior.
Understanding cryogenic toughness requires combining two types of experiments: stress/strain and impact testing to test the material's properties and a high-resolution imaging method to know how the forces applied to the material have impacted its structure at the atomistic level.
Standard testing on possible cryogenic materials includes mechanical strength, elongation measurements, and Charpy impact toughness. This criterion evaluates the energy a test specimen absorbs when breaking under an impact force. Such tests can be conducted at ambient temperature or under cryogenic conditions.
Scanning electron microscopy, electron backscatter diffraction (EBSD), and X-ray computed tomography (CT) are all imaging technologies for defect evaluation that can be used to analyze the material's structure at the micrometer scale. X-rayWhen combined with the appropriate image processing and segmentation tools, X-ray tomography can be used to see and dissect a whole 3D image. Finally, each flaw can be statistically quantified, allowing for informed decisions to optimize material performance.
Austenitic steel is a commonly used cryogenic material suitable for various applications. Several forms of austenitic steel exist, but the presence of alloying metals such as nickel and chrome distinguishes them. Some kinds also contain traces of molybdenum and titanium.
Recently, researchers discovered that fine-grained Fe-30Mn-0.11C, a type of austenitic steel, has an unusually high cryogenic toughness. The research team employed a range of experimental methodologies and mechanical property testing to establish why this low-cost austenitic steel type behaved so unusually.
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