@article{xu_dycus_lebeau_2018, title={Numerical modeling of specimen geometry for quantitative energy dispersive X-ray spectroscopy}, volume={184}, ISSN={["1879-2723"]}, DOI={10.1016/j.ultramic.2017.08.015}, abstractNote={Transmission electron microscopy specimens typically exhibit local distortion at thin foil edges, which can influence the absorption of X-rays for quantitative energy dispersive X-ray spectroscopy (EDS). Here, we report a numerical, three-dimensional approach to model the geometry of general specimens and its influence on quantification when using single and multiple detector configurations. As a function of specimen tilt, we show that the model correctly predicts the asymmetric nature of X-ray counts and ratios. When using a single detector, we show that complex specimen geometries can introduce significant uncertainty in EDS quantification. Further, we show that this uncertainty can be largely negated by collection with multiple detectors placed symmetrically about the sample such as the FEI Super-X configuration. Based on guidance provided by the model, we propose methods to reduce quantification error introduced by the sample shape. The source code is available at https://github.com/subangstrom/superAngle.}, journal={ULTRAMICROSCOPY}, author={Xu, W. and Dycus, J. H. and LeBeau, J. M.}, year={2018}, month={Jan}, pages={100–108} }
 @article{xu_zhang_cheng_mathaudhu_scattergood_koch_lavernia_zhu_2017, title={On the origin and behavior of irradiation-induced c-component dislocation loops in magnesium}, volume={131}, ISSN={["1873-2453"]}, url={https://doi.org/10.1016/j.actamat.2017.04.015}, DOI={10.1016/j.actamat.2017.04.015}, abstractNote={C-component dislocation loops are one of the unique defects in hexagonal close-packed (hcp) crystals that promote the accelerated growth and void formation under irradiation. Here, we report in situ observation of c-component dislocation loop formation in Mg under electron irradiation with emphasis on their atomic structures. Aberration-corrected scanning transmission electron microscopy imaging is utilized to reveal four possible types of double-layer loops, which were identified as different types of stacking fault and dislocation core structures. Triple- and quadruple-layer c-component dislocation loops were also observed. The formation mechanisms of the four types of double-layer loops were revealed via molecular dynamics simulations. The experimentally observed formation rate of the single- and double-layer dislocation loops is controlled by their formation energies. Our direct experimental observations in combination with molecular dynamics simulations provide fundamental insight into the mechanisms governing nucleation and growth of the c-component dislocation loops as well as their interactions, which could potentially help with future development of irradiation-resistant materials.}, journal={ACTA MATERIALIA}, publisher={Elsevier BV}, author={Xu, Weizong and Zhang, Yongfeng and Cheng, Guangming and Mathaudhu, Suveen N. and Scattergood, Ronald O. and Koch, Carl C. and Lavernia, Enrique J. and Zhu, Yuntian}, year={2017}, month={Jun}, pages={457–466} }
 @article{xu_dycus_sang_lebeau_2016, title={A numerical model for multiple detector energy dispersive X-ray spectroscopy in the transmission electron microscope}, volume={164}, ISSN={["1879-2723"]}, DOI={10.1016/j.ultramic.2016.02.004}, abstractNote={Here we report a numerical approach to model a four quadrant energy dispersive X-ray spectrometer in the transmission electron microscope. The model includes detector geometries, specimen position and absorption, shadowing by the holder, and filtering by the Be carrier. We show that this comprehensive model accurately predicts absolute counts and intensity ratios as a function of specimen tilt and position. We directly compare the model to experimental results acquired with a FEI Super-X EDS four quadrant detector. The contribution from each detector to the sum is investigated. The program and source code can be downloaded from https://github.com/subangstrom/superAngle.}, journal={ULTRAMICROSCOPY}, author={Xu, W. and Dycus, J. H. and Sang, X. and LeBeau, J. M.}, year={2016}, month={May}, pages={51–61} }
 @article{narayan_bhaumik_xu_2016, title={Direct conversion of h-BN into c-BN and formation of epitaxial c-BN/diamond heterostructures}, volume={119}, number={18}, journal={Journal of Applied Physics}, author={Narayan, J. and Bhaumik, A. and Xu, W. Z.}, year={2016} }
 @article{xu_li_valdez_saber_zhu_koch_scattergood_2016, title={Effect of nano-oxide particle size on radiation resistance of iron-chromium alloys}, volume={469}, ISSN={["1873-4820"]}, DOI={10.1016/j.jnucmat.2015.11.044}, abstractNote={Radiation resistance of Fe–14Cr alloys under 200 keV He irradiation at 500 °C was systematically investigated with varying sizes of nano oxide Zr, Hf and Cr particles. It is found that these nano oxide particles acted as effective sites for He bubble formation. By statistically analyzing 700–1500 He bubbles at the depth of about 150–700 nm from a series of HRTEM images for each sample, we established the variation of average He bubble size, He bubble density, and swelling percentage along the depth, and found them to be consistent with the He concentration profile calculated from the SIRM program. Oxide particles with sizes less than 3.5–4 nm are found most effective for enhancing radiation resistance in the studied alloy systems.}, journal={JOURNAL OF NUCLEAR MATERIALS}, author={Xu, Weizong and Li, Lulu and Valdez, James A. and Saber, Mostafa and Zhu, Yuntian and Koch, Carl C. and Scattergood, Ronald O.}, year={2016}, month={Feb}, pages={72–81} }
 @article{cheng_xu_wang_misra_zhu_2016, title={Grain size effect on radiation tolerance of nanocrystalline Mo}, volume={123}, ISSN={["1359-6462"]}, DOI={10.1016/j.scriptamat.2016.06.007}, abstractNote={We report a significant grain size effect on radiation tolerance of nanocrystalline Mo under He ion irradiation. Irradiation-induced dislocation loops mainly contribute to the irradiation-induced hardening of Mo films with grain size of > 90 nm, while few such loops in those with grain size of < 90 nm. The hardness increment after irradiation decreases with decreasing the grain size, and approaches zero at the grain size of 25 nm. Also, the size and the density of irradiation-induced He bubbles decrease as the grain size decreases. This observation provides direct evidence that nanocrystalline body-centered-cubic metals have greater radiation tolerance than their ultra-fine-grained or coarse-grained counterparts.}, journal={SCRIPTA MATERIALIA}, author={Cheng, G. M. and Xu, W. Z. and Wang, Y. Q. and Misra, A. and Zhu, Y. T.}, year={2016}, month={Oct}, pages={90–94} }
 @article{xu_bowes_grimley_irving_lebeau_2016, title={In-situ real-space imaging of single crystal surface reconstructions via electron microscopy}, volume={109}, ISSN={["1077-3118"]}, url={http://dx.doi.org/10.1063/1.4967978}, DOI={10.1063/1.4967978}, abstractNote={Crystal surfaces are sensitive to the surrounding environment, where atoms left with broken bonds reconstruct to minimize surface energy. In many cases, the surface can exhibit chemical properties unique from the bulk. These differences are important as they control reactions and mediate thin film growth. This is particularly true for complex oxides where certain terminating crystal planes are polar and have a net dipole moment. For polar terminations, reconstruction of atoms on the surface is the central mechanism to avoid the so called polar catastrophe. This adds to the complexity of the reconstruction where charge polarization and stoichiometry govern the final surface in addition to standard thermodynamic parameters such as temperature and partial pressure. Here we present direct, in-situ determination of polar SrTiO3 (110) surfaces at temperatures up to 900 C using cross-sectional aberration corrected scanning transmission electron microscopy (STEM). Under these conditions, we observe the coexistence of various surface structures that change as a function of temperature. As the specimen temperature is lowered, the reconstructed surface evolves due to thermal mismatch with the substrate. Periodic defects, similar to dislocations, are found in these surface structures and act to relieve stress due to mismatch. Combining STEM observations and electron spectroscopy with density functional theory, we find a combination of lattice misfit and charge compensation for stabilization. Beyond the characterization of these complex reconstructions, we have developed a general framework that opens a new pathway to simultaneously investigate the surface and near surface regions of single crystals as a function of environment.}, number={20}, journal={APPLIED PHYSICS LETTERS}, author={Xu, Weizong and Bowes, Preston C. and Grimley, Everett D. and Irving, Douglas L. and LeBeau, James M.}, year={2016}, month={Nov} }
 @article{dycus_xu_sang_d'alfonso_chen_weyland_allen_findlay_lebeau_2016, title={Influence of experimental conditions on atom column visibility in energy dispersive X-ray spectroscopy}, volume={171}, journal={Ultramicroscopy}, author={Dycus, J. H. and Xu, W. and Sang, X. and D'Alfonso, A. J. and Chen, Z. and Weyland, M. and Allen, L. J. and Findlay, S. D. and LeBeau, J. M.}, year={2016}, pages={1–7} }
 @article{chen_weyland_sang_xu_dycus_lebeau_d'alfonso_allen_findlay_2016, title={Quantitative atomic resolution elemental mapping via absolute-scale energy dispersive X-ray spectroscopy}, volume={168}, ISSN={["1879-2723"]}, DOI={10.1016/j.ultramic.2016.05.008}, abstractNote={Quantitative agreement on an absolute scale is demonstrated between experiment and simulation for two-dimensional, atomic-resolution elemental mapping via energy dispersive X-ray spectroscopy. This requires all experimental parameters to be carefully characterized. The agreement is good, but some discrepancies remain. The most likely contributing factors are identified and discussed. Previous predictions that increasing the probe forming aperture helps to suppress the channelling enhancement in the average signal are confirmed experimentally. It is emphasized that simple column-by-column analysis requires a choice of sample thickness that compromises between being thick enough to yield a good signal-to-noise ratio while being thin enough that the overwhelming majority of the EDX signal derives from the column on which the probe is placed, despite strong electron scattering effects.}, journal={ULTRAMICROSCOPY}, author={Chen, Z. and Weyland, M. and Sang, X. and Xu, W. and Dycus, J. H. and LeBeau, J. M. and D'Alfonso, A. J. and Allen, L. J. and Findlay, S. D.}, year={2016}, month={Sep}, pages={7–16} }
 @article{dycus_xu_lichtenwalner_hull_palmour_lebeau_2016, title={Structure and chemistry of passivated SiC/SiO2 interfaces}, volume={108}, ISSN={["1077-3118"]}, DOI={10.1063/1.4951677}, abstractNote={Here, we report on the chemistry and structure of 4H-SiC/SiO2 interfaces passivated either by nitric oxide annealing or Ba deposition. Using aberration corrected scanning transmission electron microscopy and spectroscopy, we find that Ba and N remain localized at SiC/SiO2 interface after processing. Further, we find that the passivating species can introduce significant changes to the near-interface atomic structure of SiC. Specifically, we quantify significant strain for nitric oxide annealed sample where Si dangling bonds are capped by N. In contrast, strain is not observed at the interface of the Ba treated samples. Finally, we place these results in the context of field effect mobility.}, number={20}, journal={APPLIED PHYSICS LETTERS}, author={Dycus, J. Houston and Xu, Weizong and Lichtenwalner, Daniel J. and Hull, Brett and Palmour, John W. and LeBeau, James M.}, year={2016}, month={May} }
 @article{ma_xu_zhou_moering_narayan_zhu_2015, title={Alloying effect on grain-size dependent deformation twinning in nanocrystalline Cu-Zn alloys}, volume={95}, ISSN={["1478-6443"]}, DOI={10.1080/14786435.2014.1000418}, abstractNote={Grain-size dependency of deformation twinning has been previously reported in nanocrystalline face-centred-cubic metals, which results in an optimum grain-size range for twin formation. Here, we report, for the first time in experiments, the observed optimum grain sizes for deformation twins in nanocrystalline Cu–Zn alloys which slightly increase with increasing Zn content. This result agrees with the reported trend but is much weaker than predicted by stacking-fault-energy based models. Our results indicate that alloying changes the relationship between the stacking-fault and twin-fault energy and therefore affects the optimum grain size for deformation twinning. These observations should be also applicable to other alloy systems.}, number={3}, journal={PHILOSOPHICAL MAGAZINE}, author={Ma, X. L. and Xu, W. Z. and Zhou, H. and Moering, J. A. and Narayan, J. and Zhu, Y. T.}, year={2015}, month={Jan}, pages={301–310} }
 @article{zhou_cheng_ma_xu_mathaudhu_wang_zhu_2015, title={Effect of Ag on interfacial segregation in Mg-Gd-Y-(Ag)-Zr alloy}, volume={95}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2015.05.020}, abstractNote={Abstract Interfaces such as twin boundaries, stacking faults and grain boundaries often play an important role in controlling mechanical properties of metals through interaction with dislocations. Segregation of alloy elements and impurities to these interfaces can stabilize them and produce a large strengthening effect. Here we report the effect of Ag on segregation of alloy elements at twin boundaries, stacking faults and grain boundaries in the Mg–Gd system. Specifically, for the first time a spinal-shaped periodic segregation is observed at the {1 0  1 ¯  2} twin boundary and high-angle lamellar grain boundary in the Mg–Gd–Y–Zr alloy due to the presence of the Ag addition. The segregation consists of Gd- and Ag-rich columns. It appears that high Ag content in the spinal-shaped segregation induces fcc-like cell structures.}, journal={ACTA MATERIALIA}, author={Zhou, H. and Cheng, G. M. and Ma, X. L. and Xu, W. Z. and Mathaudhu, S. N. and Wang, Q. D. and Zhu, Y. T.}, year={2015}, month={Aug}, pages={20–29} }
 @article{zhou_wang_guo_ye_jian_xu_ma_moering_2015, title={Finite element simulation and experimental investigation on homogeneity of Mg-9.8Gd-2.7Y-0.4Zr magnesium alloy processed by repeated-upsetting}, volume={225}, ISSN={["0924-0136"]}, DOI={10.1016/j.jmatprotec.2015.06.010}, abstractNote={Abstract A novel severe plastic deformation (SPD) process called repeated-upsetting (RU), which produces homogenous samples of large size, is employed to process a high performance magnesium alloy Mg-9.8Gd-2.7Y-0.4Zr at 350 °C with 1–4 passes. Homogenous microstructure and mechanical properties can be achieved after 4 passes of RU. Experimental and finite-element modeling results show that effective strain accumulation with more passes can improve both grain refinement and micro-hardness of samples.}, journal={JOURNAL OF MATERIALS PROCESSING TECHNOLOGY}, author={Zhou, H. and Wang, Q. D. and Guo, W. and Ye, B. and Jian, W. W. and Xu, W. Z. and Ma, X. L. and Moering, J.}, year={2015}, month={Nov}, pages={310–317} }
 @article{li_xu_saber_zhu_koch_scattergood_2015, title={Influence of scandium addition on the high-temperature grain size stabilization of oxide-dispersion-strengthened (ODS) ferritic alloy}, volume={636}, ISSN={["1873-4936"]}, DOI={10.1016/j.msea.2015.03.117}, abstractNote={The influence of 1–4 at% Sc addition on the thermal stability of mechanically alloyed ODS ferritic alloy was studied in this work. Sc addition was found to significantly stabilize grain size and microhardness at high temperatures. Grain sizes of samples with 1 and 4 at% Sc was found maintained in the nanoscale range at temperatures up to 1000 °C with hardness maintained at 5.6 and 6.7 GPa, respectively. The detailed microstructure was also investigated from EDS elemental mapping, where nanofeatures [ScTiO] were observed, while nanosized [YTiO] particles were rarely seen. This is probably due to the concentration difference between Sc and Y, leading to the formation of [ScTiO] favoring that of [YTiO]. Precipitation was considered as the major source for the observed high temperature stabilization. In addition, 14YT–Sc alloys without large second phases such as Ti-oxide can exhibit better performance compared to conventional ODS materials.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Li, Lulu and Xu, Weizong and Saber, Mostafa and Zhu, Yuntian and Koch, Carl C. and Scattergood, Ronald O.}, year={2015}, month={Jun}, pages={565–571} }
 @article{li_xu_saber_zhu_koch_scattergood_2015, title={Long-term stability of 14YT-4Sc alloy at high temperature}, volume={647}, ISSN={["1873-4936"]}, DOI={10.1016/j.msea.2015.09.012}, abstractNote={14YT alloy (Fe–14Cr–0.25wt%Y2O3–0.4wt%Ti) with 4 at% Sc addition was previously reported to exhibit a nanoscale microstructure and high strength when annealed at temperatures up to 1000 °C (0.65Tm) for 1 h. Here we report that the microstructure and mechanical behavior of 14YT–4Sc alloy after long-term annealing for up to 60 h at 1000 °C. FIB analysis shows abnormal grain growth with annealing time, while a large fraction of the matrix still consists of nanoscale grains. TEM images reveal a slight growth of nano grains, with estimated grain growth exponent, n, to be 0.29. Sc–Ti–Y–O enriched nano oxide particles (<10 nm) were observed in EDS mapping of the 14YT–4Sc–60h sample. The nano-structure retention at the high temperature of 1000 °C for 60 h is attributed to these complex nano oxides.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Li, Lulu and Xu, Weizong and Saber, Mostafa and Zhu, Yuntian and Koch, Carl C. and Scattergood, Ronald O.}, year={2015}, month={Oct}, pages={222–228} }
 @article{xu_li_saber_koch_zhu_scattergood_2015, title={Microstructures and Stabilization Mechanisms of Nanocrystalline Iron-Chromium Alloys with Hafnium Addition}, volume={46A}, ISSN={["1543-1940"]}, DOI={10.1007/s11661-015-2985-2}, number={9}, journal={METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE}, author={Xu, Weizong and Li, Lulu and Saber, Mostafa and Koch, Carl C. and Zhu, Yuntian and Scattergood, Ronald O.}, year={2015}, month={Sep}, pages={4394–4404} }
 @article{ma_huang_xu_zhou_wu_zhu_2015, title={Strain hardening and ductility in a coarse-grain/nanostructure laminate material}, volume={103}, ISSN={["1359-6462"]}, DOI={10.1016/j.scriptamat.2015.03.006}, abstractNote={A laminate structure with a nanostructured Cu–10Zn layer sandwiched between two coarse-grained Cu layers was produced by high-pressure torsion, rolling and annealing. Sharp interlayer interfaces with sufficient bonding strength were developed. Mechanical incompatibility between different layers during tensile deformation produced high strain hardening, which led to a tensile ductility higher than prediction by the rule-of-mixture. These observations provide insights into the architectural design and deformation studies of materials with gradient and laminate structures.}, journal={SCRIPTA MATERIALIA}, author={Ma, X. L. and Huang, C. X. and Xu, W. Z. and Zhou, H. and Wu, X. L. and Zhu, Y. T.}, year={2015}, month={Jul}, pages={57–60} }
 @article{zhang_wang_xu_zhang_li_bradford_zhu_2015, title={Strong and Conductive Dry Carbon Nanotube Films by Microcombing}, volume={11}, ISSN={["1613-6829"]}, DOI={10.1002/smll.201500111}, abstractNote={In order to maximize the carbon nanotube (CNT) buckypaper properties, it is critical to improve their alignment and reduce their waviness. In this paper, a novel approach, microcombing, is reported to fabricate aligned CNT films with a uniform structure. High level of nanotube alignment and straightness was achieved using sharp surgical blades with microsized features at the blade edges to comb single layer of CNT sheet. These microcombs also reduced structural defects within the film and enhanced the nanotube packing density. Following the microcombing approach, the as-produced CNT films demonstrated a tensile strength of up to 3.2 GPa, Young's modulus of up to 172 GPa, and electrical conductivity of up to 1.8 × 10(5) S m(-1) , which are much superior to previously reported CNT films or buckypapers. More importantly, this novel technique requires less rigorous process control and can construct CNT films with reproducible properties.}, number={31}, journal={SMALL}, author={Zhang, Liwen and Wang, Xin and Xu, Weizong and Zhang, Yongyi and Li, Qingwen and Bradford, Philip D. and Zhu, Yuntian}, year={2015}, month={Aug}, pages={3830–3836} }
 @article{zhou_xu_jian_cheng_ma_guo_mathaudhu_wang_zhu_2014, title={A new metastable precipitate phase in Mg-Gd-Y-Zr alloy}, volume={94}, ISSN={["1478-6443"]}, DOI={10.1080/14786435.2014.913115}, abstractNote={Mg–RE alloys are among the strongest Mg-based alloys due to their unique precipitation structures. A previously unobserved metastable phase (βT) is found to coexist with reported β″ and β′ metastable phases under peak ageing conditions in a Mg–Gd–Y–Zr alloy. The position of the RE elements within the βT phase is identified using atomic-resolution high-angle annular dark field scanning transmission electron microscopy imaging, and the βT phase is shown to have an orthorhombic structure with a stoichiometry of Mg5RE. Based on these observations, a new precipitation sequence is proposed.}, number={21}, journal={PHILOSOPHICAL MAGAZINE}, author={Zhou, H. and Xu, W. Z. and Jian, W. W. and Cheng, G. M. and Ma, X. L. and Guo, W. and Mathaudhu, S. N. and Wang, Q. D. and Zhu, Y. T.}, year={2014}, pages={2403–2409} }
 @article{li_saber_xu_zhu_koch_scattergood_2014, title={High-temperature grain size stabilization of nanocrystalline Fe-Cr alloys with Hf additions}, volume={613}, ISSN={["1873-4936"]}, DOI={10.1016/j.msea.2014.06.099}, abstractNote={Abstract The influence of 1–4 at% Hf additions on the thermal stability of mechanically alloyed nanocrystalline Fe–14Cr alloys was studied in this work. XRD-calculated grain size and microhardness results were reported versus isochronal annealing treatments up to 1100 °C. Microstructural evolution was investigated using channeling contrast FIB imaging and TEM. Grain size of samples with 4 at% Hf was found to be maintained in the nanoscale range at temperatures up to 1000 °C. Zener pinning was considered as a major source of high temperature grain size stabilization. By comparing the Orowan strengthening contribution to the total hardness, the deviation of grain size predictions from the actual grain size in Fe–14Cr–4Hf suggests the presence of thermodynamic stabilization by the solute segregation to grain boundaries (GBs). A predictive thermodynamic model indicates that the thermodynamic stabilization can be expected.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Li, Lulu and Saber, Mostafa and Xu, Weizong and Zhu, Yuntian and Koch, Carl C. and Scattergood, Ronald O.}, year={2014}, month={Sep}, pages={289–295} }
 @article{xu_li_saber_koch_zhu_scattergood_2014, title={Nano ZrO2 particles in nanocrystalline Fe-14Cr-1.5Zr alloy powders}, volume={452}, ISSN={["1873-4820"]}, DOI={10.1016/j.jnucmat.2014.05.067}, abstractNote={Here we report on the formation of nano ZrO2 particles in Fe–14Cr–1.5Zr alloy powders synthesized by mechanical alloying. The nano ZrO2 particles were found uniformly dispersed in the ferritic matrix powders with an average size of about 3.7 nm, which rendered the alloy powders so stable that it retained nanocrystalline structure after annealing at 900 C for 1 h. The ZrO2 nanoparticles have a tetragonal crystal structure and the following orientation relationship with the matrix: (0 0 2)ZrO2//(0 0 2)Matrix and [0 1 0]ZrO2//[1 2 0]Matrix. The size and dispersion of the ZrO2 particles are comparable to those of Y–Ti–O enriched oxides reported in irradiation-resistant ODS alloys. This suggests a potential application of the new alloy powders for nuclear energy applications.}, number={1-3}, journal={JOURNAL OF NUCLEAR MATERIALS}, author={Xu, W. Z. and Li, L. L. and Saber, M. and Koch, C. C. and Zhu, Y. T. and Scattergood, R. O.}, year={2014}, month={Sep}, pages={434–439} }
 @article{piyawit_xu_mathaudhu_freudenberger_rigsbee_zhu_2014, title={Nucleation and growth mechanism of Ag precipitates in a CuAgZr alloy}, volume={610}, ISSN={["1873-4936"]}, DOI={10.1016/j.msea.2014.05.023}, abstractNote={CuAgZr alloy is a variant of the CuAg alloy that is developed for high strength and high conductivity applications. Its strengthening is accomplished mainly by the precipitation of Ag precipitates, which tend to align on {111} planes in the Cu matrix. This alignment has been reported to be caused by stacking faults on {111} planes. Contrary to these reports, this research presents evidence for Ag precipitates formation on {111} planes due to the minimization of elastic energy. The Ag precipitates were formed by clustering of Ag atoms while maintaining the fcc crystal structure of the matrix. They have faceted {111} interfaces with the matrix. The thickening of precipitates appears to be by the ledge growth mechanism, which is resulted in by misfit dislocation networks on the interface.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Piyawit, W. and Xu, W. Z. and Mathaudhu, S. N. and Freudenberger, J. and Rigsbee, J. M. and Zhu, Y. T.}, year={2014}, month={Jul}, pages={85–90} }
 @article{saber_xu_li_zhu_koch_scattergood_2014, title={Size effect of primary Y2O3 additions on the characteristics of the nanostructured ferritic ODS alloys: Comparing as-milled and as-milled/annealed alloys using S/TEM}, volume={452}, ISSN={["1873-4820"]}, DOI={10.1016/j.jnucmat.2014.05.014}, abstractNote={The need for providing S/TEM evidence to clarify the mechanisms of nano-scale precipitate formation was the motivation of this investigation. In this study, an Fe–14Cr–0.4Ti alloy was ball-milled with different amounts of Y2O3 content up to 10 wt.%, and then annealed at temperatures up to 1100 °C. Micron-size Y2O3 particles were substituted for the nano-size counterpart to elucidate the mechanism of oxide precipitate formation. The S/TEM studies revealed that the microstructure of the alloy with 10 wt.% yttria contained amorphous undissolved Y2O3 after ball milling, while a small part of the initial oxide particles were dissolved into the solid solution. Consequently, when the amount of yttria was reduced to 1 wt.%, the amorphous phase of the yttria vanished and the whole content of Y2O3 was dissolved into the BCC solid solution. Defect analysis of precipitates on the annealed samples via S/TEM and micro-hardness studies revealed that the use of micron-size primary oxide particles can produce nano-size precipitates, stable up to temperatures as high as 1100 °C, and uniformly distributed throughout the microstructure. This study indicates that the use of high energy ball milling along with micron-size primary oxide particles can lead to nanostructured ferritic ODS alloys without the use of nano-size primary oxide additions.}, number={1-3}, journal={JOURNAL OF NUCLEAR MATERIALS}, author={Saber, Mostafa and Xu, Weizong and Li, Lulu and Zhu, Yuntian and Koch, Carl C. and Scattergood, Ronald O.}, year={2014}, month={Sep}, pages={223–229} }
 @article{cheng_xu_jian_yuan_tsai_zhu_zhang_millett_2013, title={Dislocations with edge components in nanocrystalline bcc Mo}, volume={28}, DOI={10.1557/jmr.2012.403}, number={13}, journal={Journal of Materials Research}, author={Cheng, G. M. and Xu, W. Z. and Jian, W. W. and Yuan, H. and Tsai, M. H. and Zhu, Y.T. and Zhang, Y. F. and Millett, P. C.}, year={2013}, pages={1820–1826} }
 @article{wang_jiang_xu_cai_inoue_zhu_2013, title={Effect of carbon nanotube length on thermal, electrical and mechanical properties of CNT/bismaleimide composites}, volume={53}, ISSN={["1873-3891"]}, DOI={10.1016/j.carbon.2012.10.041}, abstractNote={Multi-wall carbon nanotubes (MWCNTs) with lengths of 0.65–1.3 mm were used to fabricate aligned and continuous MWCNT/bismaleimide composites. We found that longer CNTs resulted in higher thermal and electrical conductivities of the composites. The tensile strength and Young’s modulus, however, exhibited no CNT length dependency. Investigation of the CNT morphology by transmission electron microscopy revealed that the average nanotube diameter and wall number also increased with the CNT length, while the aspect ratio remained nearly unchanged. The structural changes significantly affected the phonon and electron transport in the composite structure, but the interplay of increased CNT length and diameter led to no appreciable change in the mechanical properties of the composites.}, journal={CARBON}, author={Wang, Xin and Jiang, Qian and Xu, Weizong and Cai, Wei and Inoue, Yoku and Zhu, Yuntian}, year={2013}, month={Mar}, pages={145–152} }
 @article{xu_zhang_cheng_jian_millett_koch_mathaudhu_zhu_2013, title={In-situ atomic-scale observation of irradiation-induced void formation}, volume={4}, ISSN={["2041-1723"]}, DOI={10.1038/ncomms3288}, abstractNote={The formation of voids in an irradiated material significantly degrades its physical and mechanical properties. Void nucleation and growth involve discrete atomic-scale processes that, unfortunately, are not yet well understood due to the lack of direct experimental examination. Here we report an in-situ atomic-scale observation of the nucleation and growth of voids in hexagonal close-packed magnesium under electron irradiation. The voids are found to first grow into a plate-like shape, followed by a gradual transition to a nearly equiaxial geometry. Using atomistic simulations, we show that the initial growth in length is controlled by slow nucleation kinetics of vacancy layers on basal facets and anisotropic vacancy diffusivity. The subsequent thickness growth is driven by thermodynamics to reduce surface energy. These experiments represent unprecedented resolution and characterization of void nucleation and growth under irradiation, and might help with understanding the irradiation damage of other hexagonal close-packed materials.}, journal={NATURE COMMUNICATIONS}, author={Xu, Weizong and Zhang, Yongfeng and Cheng, Guangming and Jian, Weiwei and Millett, Paul C. and Koch, Carl C. and Mathaudhu, Suveen N. and Zhu, Yuntian}, year={2013}, month={Aug} }
 @article{tsai_yuan_cheng_xu_tsai_tsai_jian_juan_shen_chuang_et al._2013, title={Morphology, structure and composition of precipitates in Al0.3CoCrCu0.5FeNi high-entropy alloy}, volume={32}, ISSN={["1879-0216"]}, DOI={10.1016/j.intermet.2012.07.036}, abstractNote={High-entropy alloy is a new class of metallic materials with great potential for many applications. However, their microstructural characteristics, particularly those of precipitates, remain poorly understood. This has hindered the establishment of structure-property relationship in these alloys. Here, we report the morphology, crystal structure and composition of the precipitates in the Al0.3CoCrCu0.5FeNi high-entropy alloy. Two types of precipitates were identified, namely the plate-like and the spherical precipitates. Their formation sequence and mechanism during the cooling process are discussed based on thermodynamics.}, journal={INTERMETALLICS}, author={Tsai, Ming-Hung and Yuan, Hao and Cheng, Guangming and Xu, Weizong and Tsai, Kun-Yo and Tsai, Che-Wei and Jian, Weiwei W. and Juan, Chien-Chang and Shen, Wan-Jui and Chuang, Ming-Hao and et al.}, year={2013}, month={Jan}, pages={329–336} }
 @article{jian_cheng_xu_koch_wang_zhu_mathaudhu_2013, title={Physics and model of strengthening by parallel stacking faults}, volume={103}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4822323}, DOI={10.1063/1.4822323}, abstractNote={We have recently reported that parallel stacking faults (SFs) can tremendously increase the strength of a magnesium alloy. The strengthening is found to increase linearly with the reciprocal of the mean SF spacing, d. In this study we analyze dislocation interactions with SFs, and then propose a physics-based model to explain the observed relationship between yield strength and SFs spacing. Similar to the empirical Hall-Petch relationship for grain size, it is expected that this strengthening mechanism will hold true for a variety of materials engineered with parallel spaced stacking faults over a wide range of fault spacing.}, number={13}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Jian, W. W. and Cheng, G. M. and Xu, W. Z. and Koch, C. C. and Wang, Q. D. and Zhu, Y. T. and Mathaudhu, S. N.}, year={2013}, month={Sep}, pages={133108} }
 @article{tsai_yuan_cheng_xu_jian_chuang_juan_yeh_lin_zhu_et al._2013, title={Significant hardening due to the formation of a sigma phase matrix in a high entropy alloy}, volume={33}, ISSN={["1879-0216"]}, DOI={10.1016/j.intermet.2012.09.022}, abstractNote={The hardening in Al0.3CrFe1.5MnNi0.5 high-entropy alloy not only nearly triples the hardness of the alloy, but also shows a quick hardening response and the absence of overaging. However, the crystal structure, morphology, and composition of the hardening phase have not yet been confirmed. Here, such information regarding the hardening phase is investigated. It was found that the hardening phase is a Cr–Mn–Fe ternary sigma phase. Unlike in conventional engineering alloys, the sigma phase is not precipitated from the matrix, instead, the whole BCC matrix transforms to sigma phase almost without changing its composition. Therefore, the hardening phenomenon is not a precipitation hardening reaction as suggested before.}, journal={INTERMETALLICS}, author={Tsai, Ming-Hung and Yuan, Hao and Cheng, Guangming and Xu, Weizong and Jian, Weiwei W. and Chuang, Ming-Hao and Juan, Chien-Chang and Yeh, An-Chou and Lin, Su-Jien and Zhu, Yuntian and et al.}, year={2013}, month={Feb}, pages={81–86} }
 @article{zheng_li_xu_zhou_mathaudhu_zhu_lavernia_2013, title={Twinning in cryomilled nanocrystalline Mg powder}, volume={93}, ISSN={["1362-3036"]}, DOI={10.1080/09500839.2013.801567}, abstractNote={Nanocrystalline (nc) Mg powder was synthesized via cryomilling. Extension twins were identified with high-resolution transmission electron microscopy in the cryomilled powders and the study presents the first evidence of twinning in unalloyed nc Mg. The formation of twins in the nc Mg is attributed to a high strain rate, the low (cryogenic) temperature and high local shear stresses present around the grain boundaries during deformation by cryomilling.}, number={8}, journal={PHILOSOPHICAL MAGAZINE LETTERS}, author={Zheng, Baolong and Li, Ying and Xu, Weizong and Zhou, Yizhang and Mathaudhu, Suveen N. and Zhu, Yuntian and Lavernia, Enrique J.}, year={2013}, month={Aug}, pages={457–464} }