NSUF - Nuclear Science User Facilities

Darryl Butt

Profile Information
Name
Dr. Darryl Butt
Institution
University of Utah
Position
Dean
Expertise
Environmental Degradation, Mechanical Properties, Sensors, Thermophysical Properties
Publications:
"A Preliminary Investigation of High Dose Ion Irradiation Response of a Lanthana-Bearing Nanostructured Ferritic Steel Processed via Spark Plasma Sintering" Somayeh Pasebani, Indrajit Charit, Ankan Guria, Yaqiao Wu, Jatuporn Burns, Darryl Butt, James Cole, Lin Shao, Journal of Nuclear Materials Vol. 495 2017 78-84 Link
A lanthana-containing nanostructured ferritic steel (NFS) was processed via mechanical alloying (MA) of Fe-14Cr-1Ti-0.3Mo-0.5La2O3 (wt.%) and consolidated via spark plasma sintering (SPS). In order to study the consolidation behavior via SPS, sintering temperature and dwell time were correlated with microstructure, density, microhardness and shear yield strength of the sintered specimens. A bimodal grain size distribution including both micron-sized and nano-sized grains was observed in the microstructure of specimens sintered at 850, 950 and 1050 oC for 45 min. Significant densification occurred at temperatures greater than 950 oC with a relative density higher than 98%. A variety of nanoparticles, some enriched in Fe and Cr oxides and copious nanoparticles smaller than 10 nm with faceted morphology and enriched in La and Ti oxides were observed. After SPS at 950 oC, the number density of Cr-Ti-La-O enriched nanoclusters with an average radius of 1.5 nm was estimated to be 1.2 ×10^24 m^-3 . The La + Ti : O ratio was close to 1 after SPS at 950 and 1050 C; however, the number density of nanoclusters decreased at 1050 C. With SPS above 950 C, the density improved but the microhardness and shear yield strength decreased due to partial coarsening of the grains and nanoparticles.
"A preliminary study on the development of La2O3-bearing nanostructured ferritic steels via high energy ball milling" Somayeh Pasebani, Indrajit Charit, Darryl Butt, James Cole, Journal of Nuclear Materials Vol. 434 2013 282-286 Link
Elemental powder mixture of Fe–Cr–Ti–Mo and La2O3 were ball milled for different milling times in a high energy shaker mill. Effects of ball milling time on crystallite size, particle size and hardness were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and microhardness tester. After 10 h of ball milling, the smallest crystallite size and highest hardness were ~24 nm and ~970 HV, respectively. Transmission electron microscopy (TEM) studies have revealed nanoscale features 2–5 nm in diameter present in the milled powder. Local atom probe tomography studies have shown that these nanoscale features were possibly nanoclusters enriched in La, TiO and O.
"Effect of Grain Boundaries on Krypton Segregation Behavior in Irradiated Uranium Dioxide" Todd Allen, Darryl Butt, Jian Gan, Lingfeng He, Hunter Henderson, Brian Jaques, Michele Manuel, Janne Pakarinen, Billy Valderrama, Journal of Metals Vol. 66 2014 2562-2568 Link
Fission products, such as krypton (Kr), are known to be insoluble within UO2, segregating toward grain boundaries and eventually leading to a lowering in thermal conductivity and fuel swelling. Recent computational studies have identi?ed that differences in grain boundary structure have a signi?cant effect on the segregation behavior of fission products. However, experimental work supporting these simulations is lacking. Atom probe tomography was used to measure the Kr distribution across grain boundaries in UO2. Polycrystalline depleted UO2 samples were irradiated with 0.7 MeV and 1.8 MeV Kr-ions and annealed to 1000C, 1300C, and 1600C for 1 h to produce a Kr-bubble dominated microstructure. The results of this work indicate a strong dependence of Kr concentration as a function of grain boundary structure. Temperature also influences grain boundary chemistry with greater Kr concentration evident at higher temperatures, resulting in a reduced Kr concentration in the bulk. Although Kr segregation takes place at elevated temperatures, no change in grain size or texture was observed in the irradiated UO2 samples.
"Lanthana-bearing nanostructured ferritic steels via spark plasma sintering" SULTAN ALSAGABI, Darryl Butt, Indrajit Charit, James Cole, Somayeh Pasebani, Yaqiao Wu, Jatuporn Burns, Kerry Allahar, Journal of Nuclear Materials Vol. 470 2016 297-306 Link
A lanthana-containing nanostructured ferritic steel (NFS) was processed via mechanical alloying (MA) of Fe-14Cr-1Ti-0.3Mo-0.5La2O3 (wt.%) and consolidated via spark plasma sintering (SPS). In order to study the consolidation behavior via SPS, sintering temperature and dwell time were correlated with microstructure, density, microhardness and shear yield strength of the sintered specimens. A bimodal grain size distribution including both micron-sized and nano-sized grains was observed in the microstructure of specimens sintered at 850, 950 and1050 °C for 45 min. Significant densification occurred at temperatures greater than 950 °C with a relative density higher than 98%. A variety of nanoparticles, some enriched in Fe and Cr oxides and copious nanoparticles smaller than 10 nm with faceted morphology and enriched in La and Ti oxides were observed. After SPS at 950 °C, the number density of Cr–Ti–La–O-enriched nanoclusters with an average radius of 1.5 nm was estimated to be 1.2 × 1024 m−3. The La + Ti:O ratio was close to 1 after SPS at 950 and 1050 °C; however, the number density of nanoclusters decreased at 1050 °C. With SPS above 950 °C, the density improved but the microhardness and shear yield strength decreased due to partial coarsening of the grains and nanoparticles.
"Mechanical Alloying of Lanthana-Bearing Nanostructured Ferritic Steels" Darryl Butt, James Cole, Somayeh Pasebani, Yaqiao Wu, Indrajit Charit, Acta Materialia Vol. 61 2013 5605-5617 Link
A novel nanostructured ferritic steel powder with the nominal composition Fe–14Cr–1Ti–0.3Mo–0.5La2O3 (wt.%) was developed via high energy ball milling. La2O3 was added to this alloy instead of the traditionally used Y2O3. The effects of varying the ball milling parameters, such as milling time, steel ball size and ball to powder ratio, on the mechanical properties and microstructural characteristics of the as-milled powder were investigated. Nanocrystallites of a body-centered cubic ferritic solid solution matrix with a mean size of approximately 20 nm were observed by transmission electron microscopy. Nanoscale characterization of the as-milled powder by local electrode atom probe tomography revealed the formation of Cr–Ti–La–O-enriched nanoclusters during mechanical alloying. The Cr:Ti:La:O ratio is considered “non-stoichiometric”. The average size (radius) of the nanoclusters was about 1 nm, with number density of 3.7x10^24 m^-3. The mechanism for formation of nanoclusters in the as-milled powder is discussed. La2O3 appears to be a promising alternative rare earth oxide for future nanostructured ferritic steels.
"Mechanical behavior of AISI 304SS determined by miniature test methods after neutron irradiation to 28 dpa" Ellen Rabenberg, Brian Jaques, Bulent Sencer, Frank Garner, Paula Freyer, T. Okita, Darryl Butt, Journal of Nuclear Materials Vol. 448 2014 315-324 Link
The mechanical properties of AISI 304 stainless steel irradiated for over a decade in the Experimental Breeder Reactor (EBR-II) were measured using miniature mechanical testing methods. The shear punch method was used to evaluate the shear strengths of the neutron-irradiated steel and a correlation factor was empirically determined to predict its tensile strength. The strength of the stainless steel slightly decreased with increasing irradiation temperature, and significantly increased with increasing dose until it saturated above approximately 5 dpa. An effective tensile strain hardening exponent was also obtained from the data which shows a relative decrease in ductility of steel with increased irradiation damage. Ferromagnetic measurements were used to observe and deduce the effects of the stress-induced austenite to martensite transformation as a result of shear punch testing.
"Microstructural stability of a self-ion irradiated lanthana-bearing nanostructured ferritic steel" SULTAN ALSAGABI, Darryl Butt, Indrajit Charit, James Cole, Somayeh Pasebani, Lin Shao, Jatuporn Burns, Lloyd Price, Journal of Nuclear Materials Vol. 462 2015 191-204 Link
Thermally stable nanofeatures with high number density are expected to impart excellent high temperature strength and irradiation stability in nanostructured ferritic steels (NFSs) which have potential applications in advanced nuclear reactors. A lanthana-bearing NFS (14LMT) developed via mechanical alloying and spark plasma sintering was used in this study. The sintered samples were irradiated by Fe2+ ions to 10, 50 and 100 dpa at 30 °C and 500 °C. Microstructural and mechanical characteristics of the irradiated samples were studied using different microscopy techniques and nanoindentation, respectively. Overall morphology and number density of the nanofeatures remained unchanged after irradiation. Average radius of nanofeatures in the irradiated sample (100 dpa at 500 °C) was slightly reduced. A notable level of irradiation hardening and enhanced dislocation activity occurred after ion irradiation except at 30 °C and ⩾50 dpa. Other microstructural features like grain boundaries and high density of dislocations also provided defect sinks to assist in defect removal.
"Processing of a novel nanostructured ferritic steel via spark plasma sintering and investigation of its mechanical and microstructural characteristics" Darryl Butt, Indrajit Charit, James Cole, Somayeh Pasebani, Yaqiao Wu, Jatuporn Burns, Kerry Allahar, INIS Repository Vol. 46 2015 Link
Nano-structured ferritic steels (NFSs) with 12-14 wt% Cr have attracted widespread interest for potential high temperature structural and fuel cladding applications in advanced nuclear reactors. They have excellent high temperature mechanical properties and high resistance to radiation-induced damage. The properties of the NFSs depend on the composition that mainly consists of Cr, Ti, W or Mo, and Y2O3 as alloying constituents. In this study, a novel nano-structured ferritic steel (Fe-14Cr-1Ti-0.3Mo-0.5La2O3, wt%) termed as 14LMT was developed via high energy ball milling and spark plasma sintering. Vickers microhardness values were measured. Microstructural studies of the developed NFSs were performed by EBSD and TEM, which revealed a bimodal grain size distribution. A significant number density of nano-precipitates was observed in the microstructure. The diameter of the precipitates varied between 2-70 nm and the morphology from the spherical to faceted shape. The Cr-La-Ti-O-enriched nano-clusters were identified by APT studies.
"Sintering Behavior of Lanthana-Bearing Nanostructured Ferritic Steel Consolidated via Spark Plasma Sintering" Darryl Butt, Indrajit Charit, James Cole, Somayeh Pasebani, Yaqiao Wu, Jatuporn Burns, Advanced Engineering Materials Vol. 18 2015 324-332 Link
Elemental powder mixture of Fe–14Cr–1Ti–0.3Mo–0.5La2O3(wt%) composition is mechanicallyalloyed for different milling durations (5, 10 and 20 h) and subsequently consolidated via spark plasmasintering under vacuum at 950?C for 7 min. The effects of milling time on the densi?cation behaviorand density/microhardness are studied. The sintering activation energy is found to be close to that ofgrain boundary diffusion. The bimodal grain structure created in the milled and sintered material isfound to be a result of milling and not of sintering alone. The oxide particle diameter varies between2 and 70 nm. Faceted precipitates smaller than 10 nm in diameter are found to be mostly La–Ti–Cr-enriched complex oxides that restrict further recrystallization and related phenomena
"Subsurface imaging of grain microstructure using picosecond ultrasonics" Darryl Butt, Hunter Henderson, David Hurley, Brian Jaques, Marat Khafizov, Andrew Nelson, Janne Pakarinen, Michele Manuel, Lingfeng He, Acta Materialia Vol. 112 2016 1476-1477 Link
We report on imaging subsurface grain microstructure using picosecond ultrasonics. This approach relies on elastic anisotropy of crystalline materials where ultrasonic velocity depends on propagation direction relative to the crystal axes. Picosecond duration ultrasonic pulses are generated and detected using ultrashort light pulses. In materials that are transparent or semitransparent to the probe wavelength, the probe monitors gigahertz frequency Brillouin oscillations. The frequency of these oscillations is related to the ultrasonic velocity and the optical index of refraction. Ultrasonic waves propagating across a grain boundary experience a change in velocity due to a change in crystallographic orientation relative to the ultrasonic propagation direction. This change in velocity is manifested as a change in the Brillouin oscillation frequency. Using the ultrasonic propagation velocity, the depth of the interface can be determined from the location in time of the transition in oscillation frequency. A subsurface image of the grain boundary is obtained by scanning the beam along the surface. We demonstrate this subsurface imaging capability using a polycrystalline UO2 sample. Cross section liftout analysis of the grain boundary using electron microscopy was used to verify our imaging results.
Presentations:
"Development of Nanostructured Ferritic Alloys Containing Lanthana-based Nanoparticles via Spark Plasma Sintering" Darryl Butt, Indrajit Charit, James Cole, TMS 2014 February 16-20, (2014)
"Processing of a Novel Nanostructured Ferritic Steel via Spark Plasma Sintering and Investigation of Its Mechanical and Microstructural Characteristics" Darryl Butt, Indrajit Charit, James Cole, Somayeh Pasebani, Yaqiao Wu, SMINS-3 October 7-10, (2013)

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The Nuclear Science User Facilities (NSUF) is the U.S. Department of Energy Office of Nuclear Energy's only designated nuclear energy user facility. Through peer-reviewed proposal processes, the NSUF provides researchers access to neutron, ion, and gamma irradiations, post-irradiation examination and beamline capabilities at Idaho National Laboratory and a diverse mix of university, national laboratory and industry partner institutions.

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