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New technique allows real-time microscopy at high heat and loading

 New technique allows real-time microscopy at high heat and loading
A look inside the in situ scanning electron microscopy heating and loading device. Credit: North Carolina State University

Researchers have 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 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, author of a paper on the work and a professor of mechanical and aerospace engineering at North Carolina State University.

" ) heating and loading, 'we can see how the microscopic changes take place throughout the process. You can see how cracks form and grow, or how microstructure transforms during the failure process. 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 o f the behavior of advanced materials. The goal was to be able to predict how a material responds to 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 stresses as high as two gigapascals — which is equivalent to 290,075 pounds per square inch.

conducted "creep-fatigue" testing on a stainless steel alloy called alloy 709, which is considered for use in nuclear reactors. [Creep-fatiguetestinginvolvesexposingmaterialstohighheatandrepeatedextendedloadswhichhelpsusunderstandhowstructureswillperformwhenplacedunderloadsinextremeenvironments"Rabieisays"Thatisclearlyimportantforapplicationssuchasnuclearreactorswhicharedesignedtooperatefordecades"TothatendRabieiandhercollaboratorstestedsamplesofalloy709attemperaturesof750degreesCwhichexperiencedrepeatedloadcyclesfromholdingtheloadforonesecondtoholdingtheloadforonehourrepeatedlyuntiltheyfailedInoneiterationwherethesamplewasrepeatedlyexposedtoaloadforonehourwithseven-secondintervalsbetweenloadstheexperimentlastedformorethan600hoursAndtheinsituSEMcaptureditall"Wewereabletousethesedatatomodelwhatalloy709'sbehaviorwouldbeoveryearsofuseinanuclearreactorAndalloy709outperformed316stainlesssteelwhichiswhatiscurrentlyusedinmanyreactors"ButwhatismostexcitinghereisthemethodologyweusedForexampleourinsituSEMtechniqueallowedustowitnesstherolethatmicro-structuraldetailscalledtwinboundariesplayincontrollingcrackgrowthinalloy709takesadetourThisdetouringeffectdelayscrackgrowthimprovingthematerial'sstrengthWithoutourinsituSEMheatingandloadingtechnologysuchobservationscouldnotbepossibleMoreoverusingthistechniqueweonlyneedsmallspecimensandcangeneratedatathatnormallytakeyearstogenerateAssuchwearesavingbothtimeandtheamountofmaterialusedtoevaluatethematerial'spropertiesandanalyzeitsfailureprocess

"The ability to capture insights is a significant advance for research into any number of new, high-performance materials, especially those designed to perform in extreme environments, "Rabiei says.

The paper," Performance of alloy 709 under creep-fatigue at various dwell times, "is published in the journal : A .

New microscopy works at extreme heat, sheds light on alloys for nuclear reactors

More information:
Amrita Lall et al. Performance of Alloy 709 under creep-fatigue at various dwell times, Materials Science and Engineering: A (2019). DOI: 10.1016 / j.msea.2019.138028

Provided by
North Carolina State University

Citation :
                                                 New technique allows real-time microscopy at high heat and loading (2019, July 8)
                                                 retrieved 9 July 2019
                                                 from https://phys.org/news/2019-07-technique-real-time-microscopy-high.html

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