|"Advanced synchrotron characterization techniques for fusion materials science" David Sprouster, J Trelewicz, Lance Snead, Daniel Morrall, Takaaki Koyanagi, X Hu, Chad Parish, Lizhen Tan, Yutai Katoh, Brian Wirth, Journal of Nuclear Materials Vol. 543 2020 152574 Link|
|"Enhanced diffusion of Cr in 20Cr-25Ni type alloys under proton irradiation at 670 °C" Tianyi Chen, Ying Yang, Li He, Beata Tyburska-Puschel, Kumar Sridharan, Haixuan Xu, Lizhen Tan, Nuclear Materials and Energy Vol. 17 2018 142-146 Link|
"Evolution dependence of vanadium nitride nanoprecipitates on directionality of ion irradiation"
Bong Goo Kim, Lizhen Tan, Gary Was,
Journal of Nuclear Materials
The influence of the directionality of Fe2+ ion irradiation on the evolution of vanadium nitride platelet–shaped nanoprecipitates at 500 °C was investigated in a ferritic alloy using transmission electron microscopy. When the ion-irradiation direction was approximately aligned with the initial particle length, particles grew longer and sectioned into shorter lengths at higher doses, resulting in increased particle densities. As ion-irradiation direction deviated from particle-length direction, some particles sectioned lengthwise and then dissolved, resulting in decreased particle densities. Surviving particles were transformed into parallelograms with a different orientation relationship with the matrix. Nanoprecipitate evolution dependence on beam-nanoprecipitate orientation is a process that may be different from reactor irradiation.
"Helium sequestration at nanoparticle-matrix interfaces in helium + heavy ion irradiated nanostructured ferritic alloys"
Yutai Katoh, Chad Parish, Lizhen Tan, Steven Zinkle, Kinga Unocic, Sosuke Kondo, Lance Snead, David Hoelzer,
Journal of Nuclear Materials
We irradiated four ferritic alloys with energetic Fe and He ions: one castable nanostructured alloy (CNA) containing Ti-W-Ta-carbides, and three nanostructured ferritic alloys (NFAs). The NFAs were: 9Cr containing Y-Ti-O nanoclusters, and two Fe-12Cr-5Al NFAs containing Y-Zr-O or Y-Hf-O clusters. All four were subjected to simultaneous dual-beam Fe + He ion implantation (650 °C, ~50 dpa, ~15 appm He/dpa), simulating fusion-reactor conditions. Examination using scanning/transmission electron microscopy (STEM) revealed high-number-density helium bubbles of ~8 nm, ~1021 m-3 (CNA), and of ~3 nm, 1023 m-3 (NFAs). STEM combined with multivariate statistical analysis data mining suggests that the precipitate-matrix interfaces in all alloys survived ~50 dpa at 650 °C and serve as effective helium trapping sites. All alloys appear viable structural material candidates for fusion or advanced fission energy systems. Among these developmental alloys the NFAs appear to sequester the helium into smaller bubbles and away from the grain boundaries more effectively than the early-generation CNA.
"High-temperature strengthening mechanisms of Laves and B2 precipitates in a novel ferritic alloy"
Tianyi Chen, Chad Parish, Ying Yang, Lizhen Tan,
Materials Science and Engineering: A
Precipitates of the Laves and B2 phases were engineered in a newly-designed advanced ferritic alloy. Under creep test at 650 °C with 120 MPa, the material showed a steady-state minimum creep rate of 1 × 10−4 h−1, about one order of magnitude lower than T91. Microstructural characterization of the ferritic alloy revealed primarily ductile and partially brittle fractures after the creep test. Coarse Laves phase (~ 1 µm) was observed associating with the brittle fracture, resulting in reduced creep ductility. However, fine Laves phase precipitates (~ 100 nm) helped the dimple-ductile fracture and strengthened the material through impeding the motion of dislocations and boundaries. Unlike the B2 precipitates remained coherent exerting the classic Orowan bypassing mechanism at the brittle location, some of the B2 precipitates at the ductile location became incoherent and can develop an attractive interaction with dislocations. This coherency change of B2 precipitates, together with the nucleation of ultrafine (~ 40 nm) Laves phase precipitates during the creep test, would compensate for the coarsening-induced loss of Orowan strengthening of coherent B2 precipitates.
|"Measurement of Irradiation-induced Swelling in Stainless Steels with a New Transmission Electron Microscopy Method" Li He, Haixuan Xu, Lizhen Tan, Paul Voyles, Kumar Sridharan, Microscopy and Microanalysis Vol. 23 2017 2234-2235 Link|
|"Microstructural evolution in Fe-20Cr-25Ni austenitic alloys under proton irradiation at 670 ºC" Tianyi Chen, Lizhen Tan, Li He, Beata Tyburska-Puschel, Kumar Sridharan, Transactions of American Nuclear Society Vol. 117 2017 581-583 Link|
"Microstructural evolution of neutron-irradiated T91 and NF616 to ~4.3 dpa at 469 °C"
Kevin Field, Bong Goo Kim, Lizhen Tan, Yong Yang, Sean Gray, Meimei Li,
Journal of Nuclear Materials
Ferritic-martensitic steels such as T91 and NF616 are candidate materials for several nuclear applications. This study evaluates radiation resistance of T91 and NF616 by examining their microstructural evolutions and hardening after the samples were irradiated in the Advanced Test Reactor to ∼4.3 displacements per atom (dpa) at an as-run temperature of 469 °C. In general, this irradiation did not result in significant difference in the radiation-induced microstructures between the two steels. Compared to NF616, T91 had a higher number density of dislocation loops and a lower level of radiation-induced segregation, together with a slightly higher radiation-hardening. Unlike dislocation loops developed in both steels, radiation-induced cavities were only observed in T91 but remained small with sub-10 nm sizes. Other than the relatively stable M23C6, a new phase (likely Sigma phase) was observed in T91 and radiation-enhanced MX → Z phase transformation was identified in NF616. Laves phase was not observed in the samples.
"Microstructural evolution of NF709 (20Cr–25Ni–1.5 MoNbTiN) under neutron irradiation"
Bong Goo Kim, Lizhen Tan, Yong Yang, Cheryl Xu, Xuan Zhang, Meimei Li,
Journal of Nuclear Materials
Because of its superior creep and corrosion resistance as compared with general austenitic stainless steels, NF709 has emerged as a candidate structural material for advanced nuclear reactors. To obtain fundamental information about the radiation resistance of this material, this study examined the microstructural evolution of NF709 subjected to neutron irradiation to 3 displacements per atom at 500 °C. Transmission electron microscopy, scanning electron microscopy, and high-energy x-ray diffraction were employed to characterize radiation-induced segregation, Frank loops, voids, as well as the formation and reduction of precipitates. Radiation hardening of ∼76% was estimated by nanoindentation, approximately consistent with the calculation according to the dispersed barrier-hardening model, suggesting Frank loops as the primary hardening source.
"Microstructure and property tailoring of castable nanostructured alloys through thermomechanical treatments"
Lizhen Tan, Chad Parish,
Journal of Nuclear Materials
Three types of microstructures, i.e., tempered-martensite (TM), ferrite (F), and dual-phase (TM + F), were developed in a castable nanostructured alloy that favors a high density of nanoprecipitates compared with the precipitates in current reduced-activation ferritic-martensitic steels. The effect of the distinct microstructures on tensile properties, Charpy impact toughness, and thermal helium desorption behavior was investigated with the full TM structure as a reference. The results indicated that the F domain in the TM + F structure governed the strength and slightly impaired the impact toughness. The full F structure exhibited the highest strength without compromising ductility, but it noticeably diminished impact toughness. All microstructures had a dominant helium desorption peak at ∼1070 °C. The higher density of nanoprecipitates and complex boundaries and dislocations in the TM + F structure enhanced the secondary helium desorption peak and extended the shoulder peak, in contrast to the full TM structure with an enlarged desorption peak associated with the ferrite-to-austenite transformation at ∼810–850 °C and the full F structure with a dominant desorption peak related to bubble migration at ∼1070 °C. These results suggest that components fabricated from functionally graded microstructures could be engineered to exploit the advantages of different microstructures for demanding application requirements.
|"Neutron irradiation induced defects and clustering in NF616 and T91" Weicheng Zhong, Tarik Saleh, Lizhen Tan, Journal of Nuclear Materials Vol. 552 2021 Link|
"Phase Stability in the Fe-Rich Fe-Cr-Ni-Zr Alloys"
Tianyi Chen, Lizhen Tan, Ying Yang,
Metallurgical and Materials Transactions A
Knowledge on phase stability in Fe-rich Fe-Cr-Ni-Zr alloys is needed for the development of Laves phase strengthened Fe-Cr-Ni-Zr ferritic alloys. These alloys show promising applications as new cladding materials of nuclear reactors due to enhanced high-temperature strength and resistance to creep and irradiation hardening. Phase stability in four Fe-rich Fe-Cr-Ni-Zr alloys was carefully investigated using scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction techniques. The samples were arc-melted and heat treated at 973.15 K (700 °C) for 1275 hours and 1273.15 K (1000 °C) for 336 hours. The experimental results showed extensive solubility of Ni in the intermetallic phases Fe23Zr6 and Fe2Zr_C15. Nickel stabilizes the Laves Fe2Zr_C15 structure more than the C36 and C14 structures. In addition to Fe23Zr6 and Fe2Zr_C15, Ni7Zr2 was found to be stable in samples with higher Ni content and lower annealing temperature. The Fe2Zr_C15 and Fe23Zr6 coexist with the body-centered cubic matrix phase in all samples regardless of compositions and temperatures.
"Stability of MX-type strengthening nanoprecipitates in ferritic steels under thermal aging, stress and ion irradiation"
Yutai Katoh, Lizhen Tan, Lance Snead, Thak Sang Byun,
The stability of MX-type precipitates is critical to retain mechanical properties of both reduced activation ferritic–martensitic (RAFM) and conventional FM steels at elevated temperatures above 500 C. The stability of TaC, TaN and VN nanoprecipitates under thermal aging (600 and 700 C), creep (600 C) and ion irradiation (Fe ion, 500 C) conditions was systematically studied in this work. The statistical particle evolution in density and size was characterized using transmission electron microscopy. Nanoprecipitate stability under the studied conditions manifested differently through either dissolution, reprecipitation, growth or fragmentation, with TaC exhibiting the greatest stability followed by VN and TaN in sequence. Nanoprecipitate evolution phenomena and mechanisms and the apparent disagreement of this interpretation with published literature on the subject are discussed. These findings not only help understanding the degradation mechanisms of RAFM and conventional FM steels at elevated temperatures and under stress and irradiation, but should also prove beneficial to the development of advanced RAFM steels.
"Stability of the Strengthening Nanoprecipitates in Reduced Activation Ferritic Steels Under Fe2+ Ion Irradiation"
Yutai Katoh, Lance Snead, Lizhen Tan,
Journal of Nuclear Materials
The stability of MX-type precipitates is critical to retain mechanical properties of both reduced activation ferritic–martensitic (RAFM) and conventional FM steels at elevated temperatures. Radiation resistance of TaC, TaN, and VN nanoprecipitates irradiated up to ~49 dpa at 500 °C using Fe2+ is investigated in this work. Transmission electron microscopy (TEM) utilized in standard and scanning mode (STEM) reveals the non-stoichiometric nature of the nanoprecipitates. Irradiation did not alter their crystalline nature. The radiation resistance of these precipitates, in an order of reduced resistance, is TaC, VN, and TaN. Particle dissolution, growth, and reprecipitation were the modes of irradiation-induced instability. Irradiation also facilitated formation of Fe2W type Laves phase limited to the VN and TaN bearing alloys. This result suggests that nitrogen level should be controlled to a minimal level in alloys to gain greater radiation resistance of the MX-type precipitates at similar temperatures as well as postpone the formation and subsequent coarsening of Laves phase.
|"Ion Irradiation Defects in Austenitic Alloy 709 and Ferritic-Martensitic Steel Grade 92 for Nuclear Applications" Li He, Rigen Mo, Beata Tyburska-Puschel, Kumar Sridharan, Haixuan Xu, Tianyi Chen, Lizhen Tan, MRS Spring 2017 April 17-21, (2017)|
|"Radiation response of Grade 92 ferritic-martensitic steel irradiated up to 14.63 dpa at ~700°C" Weicheng Zhong, Lizhen Tan, TMS 2020 Annual Meeting & Exhibition February 23-27, (2020) Link|
|"Stability of MX Nanoprecipitates in Ferritic Steels Under Thermal, Stress, and Ion Irradiation" Yutai Katoh, Lance Snead, Lizhen Tan, Gary Was, 16th International Conference on Fusion Reactor Materials (ICFRM-16) October 20-26, (2013)|
|"Study of B2 and Laves Phase E volution in a Novel Ferr itic Steel under Ion Irradiation" Li He, Lizhen Tan, Ying Yang, Kumar Sridharan, MiNES (Materials in Nuclear Energy Systems) 2019 October 6-10, (2019)|
|U.S. Department of Energy Announces FY17 CINR FOA Awards - DOE selected 14 NSUF projects DOE selected five university, four national laboratory, and five industry-led projects that will take advantage of NSUF capabilities to investigate important nuclear fuel and material applications. Wednesday, September 20, 2017 - Calls and Awards|
|NSUF Researcher Feature: Kumar Sridharan - Learn more about a University of Wisconsin professor who helped kick start NSUF Sridharan's research team put the NSUF's first material samples into the ATR, launching a new era of research into the behaviors of fuels and materials in a nuclear reactor environment. Wednesday, August 28, 2019 - Newsletter, Researcher Highlight|
|DOE Awards 37 RTE Proposals - Awarded projects total nearly $1.4M in access awards Tuesday, July 14, 2020 - News Release, Calls and Awards|
This NSUF Profile is 60
Authored 10+ NSUF-supported publications
Presented an NSUF-supported publication
Submitted 3+ RTE Proposals to NSUF
Awarded 3+ RTE Proposals
Collaborated on 3+ RTE Proposals
Reviewed 10+ RTE Proposals
Morphological Response of Spherical and Platelet MX-Type Precipitates to In-Situ Ion Irradiation in Novel Fe-Based Alloys - FY 2020 RTE 2nd Call, #4200
Radiation-Hardening and Microstructural Stability of NF709 Austenitic Stainless Steel - FY 2017 RTE 1st Call, #728
Stability of Precipitates under Ion Irradiation - FY 2012 RTE Solicitation, #373
Atom Probe Tomography Investigation on the Precipitation of Neutron-Irradiated Alloy 800H/800H-TMP - FY 2019 RTE 2nd Call, #1734
Characterize Neutron Irradiated NF709 Stainless Steel Using Atom Probe Tomography - FY 2015 RTE 3rd Call, #591
Investigation of Deformation Mechanisms of an Intermetallic-strengthened Alloy with and without Heavy Ion Irradiation - FY 2017 RTE 1st Call, #804
Local Deformation Mechanism of Neutron-Irradiated NF709 Austenitic Stainless Steel - FY 2019 RTE 1st Call, #1652
Radiation effect to the deformation mechanism of Alloys 800H and 800H-TMP - FY 2020 RTE 2nd Call, #4094
Radiation-Hardening and Microstructural Stability of NF709 Austenitic Stainless Steel - FY 2017 RTE 3rd Call, #1014