|"A review of the irradiation evolution of dispersed oxide nanoparticles in the b.c.c. Fe-Cr system: Current understanding and future directions" Janelle Wharry, Matthew Swenson, Kayla Yano, Journal of Nuclear Materials Vol. 486 2017 11-20 Link|
"Correlative STEM-APT characterization of radiation-induced segregation and precipitation of in-service BWR 304 stainless steel"
Timothy Lach, Kayla Yano, Danny Edwards, Thak Sang Byun, Peter Chou,
Journal of Nuclear Materials
Radiation induced segregation and precipitation phenomena in an in-service boiling water reactor 304 stainless steel component were investigated using directly correlated 3D-atom probe tomography and scanning transmission electron microscopy. Significant quantitative differences in measured segregation at grain boundaries were found between the atom probe and energy dispersive spectroscopy measurements of the exact same locations. In particular, a much stronger Si segregation (~10 atomic% via atom probe versus ~4 atomic% via electron microscopy) and different Cr profile shapes were detected that are critical to models of radiation induced segregation and stress corrosion cracking behavior. These quantitative differences highlight the need for comparative microscopy and critical evaluation of limitations in each analytical method. Elemental segregation to dislocations and conjoined-clusters were also highlighted by atom probe; confirming and expanding upon what has been observed in test reactor neutron and accelerator-based ion irradiations.
|"In situ TEM mechanical testing: an emerging approach for characterization of polycrystalline, irradiated alloys" Janelle Wharry, Kayla Yano, Matthew Swenson, Yaqiao Wu, Microscopy & Microanalysis Vol. 22 2016 1478 Link|
"Intrinsic-extrinsic size effect relationship for micromechanical tests"
Janelle Wharry, Kayla Yano, Priyam Patki,
Miniaturized mechanical tests are commonly utilized to evaluate properties of materials, including thin films, nanostructured, and irradiated materials. However, the specimen size effect occurs when miniaturized sample geometries contain too few dislocation sources, resulting in elevated yield stresses. The size effect is controlled by extrinsic (specimen dimensions) and intrinsic (microstructure) factors. Here, we summarize extrinsic and in- trinsic size effects from micro-compression pillar, micro-cantilever bend, and flexure studies reported in the ar- chival literature. We find an approximately linear relationship between intrinsic and extrinsic size effects. Meaningful mechanical properties can be measured when extrinsic size dominates the intrinsic size.
|"Method for Evaluating Irradiation Effects on Flow Stress in Fe-9%Cr ODS Using TEM In Situ Cantilevers" Kayla Yano, Yaqiao Wu, Janelle Wharry, Journal of Minerals, Metals & Materials Society Vol. 72 2020 2065-2074 Link|
|"Probing the Damage Recovery Mechanism in Irradiated Stainless Steels Using In-Situ Microcantilever Bending Test" Keyou Mao, Hao Wang, Haozheng Qu, Kayla Yano, Philip Edmondson, Cheng Sun, Janelle Wharry, Frontiers in Materials Vol. 2022 Link|
"Role of cavities on deformation-induced martensitic transformation pathways in a laser-welded, neutron irradiated austenitic stainless steel"
Janelle Wharry, Keyou Mao, Cheng Sun, Ching-Heng Shiau, Kayla Yano, Paula Freyer, Anter EL-AZAB, Frank Garner, Aaron French, Lin Shao,
The role of cavities on deformation-induced martensitic phase transformations is studied in a laser-welded and neutron irradiated austenitic stainless steel. Orientation dependent nanoindentation experiments are performed in the base metal and the weld heat affected zone (HAZ) at room temperature. Transmission electron microscopy study of deformed microstructures indicates indentation-induced α’-martensite forms in the base metal, whereas α’- and ε-martensite arise in the HAZ. The different pathway of martensite phase transformation is attributed to the laser weld-induced annealing of cavities. Our results suggest that deformation-induced martensitic phase transformation of austenitic stainless steel is correlated to neutron irradiated cavity structures.
"TEM in situ cube-corner indentation analysis using ViBe motion detection algorithm"
Matthew Swenson, Janelle Wharry, Kayla Yano, Stephen Thomas, Yang Lu,
Journal of Nuclear Materials
Transmission electron microscopic (TEM) in situ mechanical testing is a promising method for understanding plasticity in shallow ion irradiated layers and other volume-limited materials. One of the simplest TEM in situ experiments is cube-corner indentation of a lamella, but the subsequent analysis and interpretation of the experiment is challenging, especially in engineering materials with complex microstructures. In this work, we: (a) develop MicroViBE, a motion detection and background subtraction-based post-processing approach, and (b) demonstrate the ability of MicroViBe, in combination with post-mortem TEM imaging, to carry out an unbiased qualitative interpretation of TEM indentation videos. We focus this work around a Fe-9%Cr oxide dispersion strengthened (ODS) alloy, irradiated with Fe2+ ions to 3 dpa at 500?°C. MicroViBe identifies changes in Laue contrast that are induced by the indentation; these changes accumulate throughout the mechanical loading to generate a “heatmap” of features in the original TEM video that change the most during the loading. Dislocation loops with b?=?½ <111> identified by post-mortem scanning TEM (STEM) imaging correspond to hotspots on the heatmap, whereas positions of dislocation loops with b?=?<100> do not correspond to hotspots. Further, MicroViBe enables consistent, objective quantitative approximation of the b?=?½ <111> dislocation loop number density.
"TEM in situ micropillar compression tests of ion irradiated oxide dispersion strengthened alloy"
Matthew Swenson, Janelle Wharry, Yaqiao Wu, Kayla Yano,
Journal of Nuclear Materials
The growing role of charged particle irradiation in the evaluation of nuclear reactor candidate materials requires the development of novel methods to assess mechanical properties in near-surface irradiation damage layers just a few micrometers thick. In situ transmission electron microscopic (TEM) mechanical testing is one such promising method. In this work, microcompression pillars are fabricated from a Fe2+ ion irradiated bulk specimen of a model Fe-9%Cr oxide dispersion strengthened (ODS) alloy. Yield strengths measured directly from TEM in situ compression tests are within expected values, and are consistent with predictions based on the irradiated microstructure. Measured elastic modulus values, once adjusted for the amount of deformation and deflection in the base material, are also within the expected range. A pillar size effect is only observed in samples with minimum dimension =100 nm due to the low inter-obstacle spacing in the as received and irradiated material. TEM in situ micropillar compression tests hold great promise for quantitatively determining mechanical properties of shallow ion-irradiated layers.
|"Understanding plasticity in irradiated alloys through TEM in situ compression pillar tests" Kayla Yano, Priyam Patki, Matthew Swenson, Journal of Materials Research Vol. 35 2020 1037-1050 Link|
|"Assessing mechanical properties of irradiated materials by nanomechanical testing" Janelle Wharry, Kayla Yano, Yaqiao Wu, ICSMA18 July 15-18, (2018)|
|"Correlation between irradiation defects and transition dimension for TEM in situ mechanical testing" Matthew Swenson, Janelle Wharry, Kayla Yano, American Nuclear Society 2017 Annual Meeting June 11-15, (2018)|
|"In Situ TEM Clamped Beam Fracture in Fe-9Cr ODS" Kayla Yano, Janelle Wharry, ANS Annual Meeting 2018 June 17-21, (2018)|
|"In situ TEM fracture testing for shallow ion irradiated layers" Janelle Wharry, Kayla Yano, Microscopy & Microanalysis 2017 April 6-7, (2017)|
|"In situ TEM mechanical testing: an emerging approach for characterization of polycrystalline, irradiated alloys" Matthew Swenson, Janelle Wharry, Yaqiao Wu, Kayla Yano, Microscopy & Microanalysis July 24-28, (2016)|
|"In situ TEM microcompression pillar size effects in Fe-9Cr ODS" Matthew Swenson, Janelle Wharry, Kayla Yano, American Nuclear Society June 12-16, (2016)|
|"Linking RIS and Grain Decohesion Using In Situ TEM 4-point Beams" Kayla Yano, Janelle Wharry, The Minerals, Metals & Materials Society 2018 March 11-15, (2018)|
|"Mechanics of irradiated alloys studied through in situ TEM testing" Janelle Wharry, Kayla Yano, Yaqiao Wu, TMS 2018 March 11-15, (2018)|
|"Method for extracting true stress from TEM in situ compression testing" Kayla Yano, Janelle Wharry, M&M 2018 August 5-9, (2018)|
|DOE awards 39 RTE Projects - Projects total approximately $1.3 million Thursday, February 1, 2018 - Calls and Awards|
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