@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{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{saber_koch_scattergood_2015, title={Thermodynamic Grain Size Stabilization Models: An Overview}, volume={3}, ISSN={["2166-3831"]}, DOI={10.1080/21663831.2014.997894}, abstractNote={Grain boundaries in a nanocrystalline microstructure produce an increase in the excess free energy of the system. Grain growth is a consequence of the thermodynamic driving force reducing this excess. Thermodynamic stabilization is an approach based on eliminating the driving force by suitable alloy additions that can produce a metastable equilibrium state at the nanoscale grain size, as opposed to kinetic stabilization where the grain growth mobility is restricted by pinning and/or drag mechanisms. The present paper reviews and compares various models proposed for thermodynamic stabilization.}, number={2}, journal={MATERIALS RESEARCH LETTERS}, author={Saber, Mostafa and Koch, Carl C. and Scattergood, Ronald O.}, year={2015}, pages={65–75} }
 @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={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{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{saber_kotan_koch_scattergood_2013, title={A predictive model for thermodynamic stability of grain size in nanocrystalline ternary alloys}, volume={114}, ISSN={["0021-8979"]}, DOI={10.1063/1.4821040}, abstractNote={This work presents a model for evaluating thermodynamic stabilization of ternary nanocrystalline alloys. It is applicable to alloy systems containing strongly segregating size-misfit solutes with a significant enthalpy of elastic strain and/or immiscible solutes with a positive mixing enthalpy. On the basis of a regular solution model, the chemical and elastic strain energy contributions are incorporated into the mixing enthalpy ΔHmix, and the mixing entropy ΔSmix is obtained using the ideal solution approximation. The Gibbs mixing free energy ΔGmix is minimized with respect to simultaneous variations in grain size and solute segregation parameters. The Lagrange multiplier method is used to obtain numerical solutions for the minimum ΔGmix corresponding to an equilibrium grain size for given alloy compositions. The numerical solutions will serve as a guideline for choosing solutes and assessing the possibility of thermodynamic stabilization. The temperature dependence of the nanocrystalline grain size and interfacial solute excess can be evaluated for selected ternary systems. Model predictions are presented using available input data for a wide range of solvent-solute combinations. The model predictions are compared to experimental results for Cu-Zn-Zr, Fe-Cr-Zr, and Fe-Ni-Zr alloys where thermodynamic stabilization might be effective.}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={Saber, Mostafa and Kotan, Hasan and Koch, Carl C. and Scattergood, Ronald O.}, year={2013}, month={Sep} }
 @article{kotan_darling_saber_scattergood_koch_2013, title={An in situ experimental study of grain growth in a nanocrystalline Fe91Ni8Zr1 alloy}, volume={48}, ISSN={["0022-2461"]}, DOI={10.1007/s10853-012-7002-1}, abstractNote={Grain growth and microstructural evolution of thermally stabilized Fe91Ni8Zr1 were investigated by in situ and ex situ studies. Our investigations suggest that the microstructural evolution is fairly slow and the microstructure shows stabilization up to about 700 °C. Above this temperature, a certain fraction of grains grow abnormally into the nanocrystalline matrix, resulting in a bimodal microstructure and causing the complete loss of thermal stability. The reason for abnormal grain growth and the loss of thermal stability is identified as the appearance of the fcc γ-phase and consequent reduction in the total area of grain boundaries and the overall stored energy.}, number={5}, journal={JOURNAL OF MATERIALS SCIENCE}, author={Kotan, Hasan and Darling, Kris A. and Saber, Mostafa and Scattergood, Ronald O. and Koch, Carl C.}, year={2013}, month={Mar}, pages={2251–2257} }
 @article{koch_scattergood_saber_kotan_2013, title={High temperature stabilization of nanocrystalline grain size: Thermodynamic versus kinetic strategies}, volume={28}, ISSN={["0884-2914"]}, DOI={10.1557/jmr.2012.429}, abstractNote={Abstract}, number={13}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Koch, Carl C. and Scattergood, Ronald O. and Saber, Mostafa and Kotan, Hasan}, year={2013}, month={Jul}, pages={1785–1791} }
 @article{kotan_darling_saber_scattergood_koch_2013, title={Thermal stability and mechanical properties of nanocrystalline Fe-Ni-Zr alloys prepared by mechanical alloying}, volume={48}, ISSN={["0022-2461"]}, DOI={10.1007/s10853-013-7652-7}, number={24}, journal={JOURNAL OF MATERIALS SCIENCE}, author={Kotan, Hasan and Darling, Kris A. and Saber, Mostafa and Scattergood, Ronald O. and Koch, Carl C.}, year={2013}, month={Dec}, pages={8402–8411} }
 @article{saber_kotan_koch_scattergood_2013, title={Thermodynamic stabilization of nanocrystalline binary alloys}, volume={113}, ISSN={["0021-8979"]}, DOI={10.1063/1.4791704}, abstractNote={The work presented here was motivated by the need to develop a predictive model for thermodynamic stabilization of binary alloys that is applicable to strongly segregating size-misfit solutes, and that can use available input data for a wide range of solvent-solute combinations. This will serve as a benchmark for selecting solutes and assessing the possible contribution of thermodynamic stabilization for development of high-temperature nanocrystalline alloys. Following a regular solution model that distinguishes the grain boundary and grain interior volume fractions by a transitional interface in a closed system, we include both the chemical and elastic strain energy contributions to the mixing enthalpy ΔHmix using an appropriately scaled linear superposition. The total Gibbs mixing free energy ΔGmix is minimized with respect to simultaneous variations in the grain-boundary volume fraction and the solute contents in the grain boundary and grain interior. The Lagrange multiplier method was used to obtain numerical solutions with the constraint of fixed total solute content. The model predictions are presented using a parametric variation of the required input parameters. Applications are then given for the dependence of the nanocrystalline grain size on temperature and total solute content for selected binary systems where experimental results suggest that thermodynamic stabilization could be effective.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Saber, Mostafa and Kotan, Hasan and Koch, Carl C. and Scattergood, Ronald O.}, year={2013}, month={Feb} }
 @article{kotan_saber_koch_scattergood_2012, title={Effect of annealing on microstructure, grain growth, and hardness of nanocrystalline Fe–Ni alloys prepared by mechanical alloying}, volume={552}, ISSN={0921-5093}, url={http://dx.doi.org/10.1016/j.msea.2012.05.045}, DOI={10.1016/j.msea.2012.05.045}, abstractNote={Fe–xNi alloys from x = 0 to x = 15 with an as-milled grain size and hardness in the range of 8–11 nm and 8.5–9.5 GPa, respectively, were synthesized by ball milling. Microstructural changes, hardness, and grain growth due to annealing were characterized using X-ray diffractometry, microhardness, focused ion beam channeling contrast imaging, and optical microscopy. It was found that the composition range of single bcc phase was extended by ball milling. Subsequent annealing of MA samples resulted in reduction of hardness and extensive grain growth. It indicates that nickel has no significant effect on thermal stabilization of iron. Retained austenite was observed for Fe–8Ni and Fe–10Ni alloys annealed in the two-phase region and effect of as-milled structure on retained austenite formation was discussed.}, journal={Materials Science and Engineering: A}, publisher={Elsevier BV}, author={Kotan, H. and Saber, M. and Koch, C.C. and Scattergood, R.O.}, year={2012}, month={Aug}, pages={310–315} }
 @article{saber_kotan_koch_scattergood_2012, title={Thermal stability of nanocrystalline Fe-Cr alloys with Zr additions}, volume={556}, ISSN={["0921-5093"]}, DOI={10.1016/j.msea.2012.07.045}, abstractNote={The primary objective of this work was to determine the influence of 1–4 at% Zr additions on the thermal stability of mechanically alloyed nanocrystalline Fe–Cr alloys containing 10 and 18 at% Cr. Grain sizes based on XRD, along with microhardness changes, are reported for isochronal annealing treatments up to 1000 °C. Microstructure investigations were done using optical microscopy, channeling contrast FIB imaging, and TEM. Grain size stabilization in the nanaoscale range was maintained up to 900 °C by adding 2 at% Zr. Kinetic pinning by nanoscale intermetallic particles was identified as one source of high temperature grain size stabilization. Intermetallic particles also contribute to strengthening in addition to the Hall–Petch effect. The analysis of microhardness, XRD data, and measured values from the TEM image for Fe-10 at% Cr with 2 at% Zr suggested that both thermodynamic and kinetic mechanisms would contribute to grain size stabilization. There was no significant difference in the results for the 10 and 18 at% Cr alloys, which indicates that the α→γ transformation does not influence the grain size stabilization.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Saber, Mostafa and Kotan, Hasan and Koch, Carl C. and Scattergood, Ronald O.}, year={2012}, month={Oct}, pages={664–670} }
 @inproceedings{koch_scattergood_kotan_saber, title={Thermal stability of nanocrystalline grain size in ternary FE-base alloys}, volume={753}, booktitle={Recrystallization and grain growth v}, author={Koch, C. C. and Scattergood, R. O. and Kotan, H. and Saber, M.}, pages={341–344} }