1. Atomic-Scale Design of Structural Materials for Fusion Environments Sponsors: LANL LDRD Program DOE-OBES LANL Director’s Fellowships Acknowledgements: J. P. Hirth, N. A. Mara, J. Wang, D. Bhattacharyya, T. Hochbauer, M. I. Baskes M. J. Demkowicz 1 A. Misra 2, R. G. Hoagland 3, M. Nastasi 2 2 MPA-CINT: Center for Integrated Nanotechnologies 3 MST-8: Structure-Property Relations Los Alamos National Laboratory Los Alamos, NM 87545 1 Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge, MA 02139 Collaborators (LANL): S. A. Maloy, T. C. Germann, Y. Q. Wang, X. Y. Liu, B. P. Uberuaga, A. F. Voter

2. Priorities, Gaps and Opportunities in materials research for fusion energy Priorities, Gaps and Opportunities in materials research for fusion energy Required: “new science-based methods incorporating improved cross- cutting fundamental knowledge of basic radiation damage mechanisms in materials” to the development of new materials “capable of sustained high performance operation in extreme fusion environment.” Priorities, Gaps and Opportunities: Towards a Long-Range Strategic Plan for Magnetic Fusion Energy, M. Greenwald et al., submitted in October 2007 to the Fusion Energy Sciences Advisory Committee (FESAC)

3. Nanocomposites for nuclear fusion S. J. Zinkle, Y. Matsukawa, Science 318, 959 (2007) H. L. Heinisch, F. Gao, R. J. Kurtz, J Nucl Mater 329-333, 924 (2004) M. J. Demkowicz et al., PRL 100, 136102 (2008) T. Hochbauer et al., JAP 98, 123516 (2005) N. A. Mara et al., Appl Phys Lett 92, 231901 (2008) G. R. Odette, M. J. Alinger, B. D. Wirth, Annu Rev Mater Res 38, 471 (2008) NFAs: Nanostructured Ferritic Alloys TMSs: Tempered Martensitic Steels

4. Nanocomposites for nuclear fusion S. J. Zinkle, Y. Matsukawa, Science 318, 959 (2007) H. L. Heinisch, F. Gao, R. J. Kurtz, J Nucl Mater 329-333, 924 (2004) M. J. Demkowicz et al., PRL 100, 136102 (2008) T. Hochbauer et al., JAP 98, 123516 (2005) N. A. Mara et al., Appl Phys Lett 92, 231901 (2008) G. R. Odette, M. J. Alinger, B. D. Wirth, Annu Rev Mater Res 38, 471 (2008) NFAs: Nanostructured Ferritic Alloys TMSs: Tempered Martensitic Steels Interfaces act as obstacles to slip and sinks for radiation induced defects Hence, nanocomposites provide orders of magnitude increase in strength and enhanced radiation damage tolerance compared to bulk materials By controlling interfaces at the atomic level, bulk nanocomposites can be tailored to the extreme operating conditions encountered in fusion reactors

5. The need for bottom-up materials design An inexhaustible variety of nanocomposites can be made by varying  Morphologies Opportunity: the nanocomposite design space is huge Challenge: an Edisonian, “hit-and-miss” design approach is infeasible Solution: a knowledge-based approach to designing nanocomposites with desired properties from the bottom-up Approach: analysis of model systems Investigate systems amenable to both experimental and modeling study Identify fundamental mechanisms of nanocomposite behavior: how does interface structure determine nanocomposite properties? Use insight gained to propose strategies for informed materials design: what interfaces should be incorporated into nanocomposites for fusion environments? Example: incoherent FCC-BCC interfaces in nanolayered composites  Length scales  Compositions

6. Looking edge-on along the interface: Cu atoms on top (light), Nb atoms below (dark) Looking down onto interface plane: Cu atoms on top (light), Nb atoms below (dark) Created by simply joining Cu and Nb in the KS OR Interfacial Cu atomic layer strained with respect to Cu (111) Interfacial Cu layer has 5% lower atomic density than Cu (111) at 0°K KS 1 KS 2 (2 interfaces) KS min These two interfaces have nearly the same interfacial enthalpies The interfacial enthalpy of this interface is about 4.5% lower M.J.Demkowicz, J. Wang, R.G. Hoagland, Dislocations in Solids, v.14, p 141, (2008). Multiplicity of interface atomic structures in FCC-BCC multilayered composites Multiplicity of interface atomic structures in FCC-BCC multilayered composites

7. These properties, together with increased defect mobility at interfaces, favor radiation-induced point defect annihilation at interfaces. Defect formation energies are substantially lower near an interface than in the perfect crystal KS 1 Within an interface, defects delocalize. Consequently, the separation distance, within which spontaneous annihilation between vacancies and interstitials occurs, is significantly larger than in perfect crystal. Defects entering an interface change the character of the interface. Change of state Low formation energies Enhanced annihilation probability M.J. Demkowicz, R.G. Hoagland and J.P. Hirth, Phys. Rev. Lett (2008) Interface defect delocalization leads to radiation resistance

8. Relating interface structure to defect properties abundance of delocalization sites Relating interface structure to defect properties abundance of delocalization sites

9. Relating interface structure to defect properties energies of defect delocalization Relating interface structure to defect properties energies of defect delocalization

10. Design of composites for radiation tolerance Ag-V Cu-Nb Cu-V Pitsch-Petch Fe-Fe 3 C Fe-W Bagaryatskii Fe-Fe 3 C 0.9 0.4 0.1 0.05 0.04 0.01 System  Mo-MgO 2.72 W-MgO 4.78 Formulation of quantitative figures of merit to guide further research and bottom-up nanocomposite design Formulation of quantitative figures of merit to guide further research and bottom-up nanocomposite design

11. Compositional: Morphological Model systems: controlled material complexity Model conditions: In situ probeEx situ probe Implantation, accelerators, spallation sources, test reactors, CTFs, etc. Quantitative figures of merit: Compare results with predictions based on figure of merit, Γ Iterate to improve accuracy of Γ or to extend its applicability Multi-scale modeling: Directly comparable with model systems and conditions Controlled irradiation environment complexity: implanted ions, corrosion, doses, dose rates, etc. Requirements for a structured research plan

12. “new science-based methods incorporating improved cross-cutting fundamental knowledge of basic radiation damage mechanisms in materials” are required for he development of new materials “capable of sustained high performance operation in extreme fusion environment” [Greenwald report] Bottom-up materials design by tailoring interface properties at the atomic scale is needed to create nanocomposites for fusion energy applications An integrated experiment/modeling research strategy based on investigation of model systems yields quantitative figures of merit for materials design A broad-based, inclusive effort: all national labs and most research universities have the resources needed to contribute Summary bottom-up materials design for fusion energy Summary