Atomic-Scale Design of Structural Materials for Fusion Environments

1. Atomic-Scale Design of Structural Materials for Fusion Environments 1Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge, MA 02139 M. J. Demkowicz1 A. Misra2, R. G. Hoagland3, M. Nastasi2 2MPA-CINT: Center for Integrated Nanotechnologies 3MST-8: Structure-Property Relations Los Alamos National Laboratory Los Alamos, NM 87545 Collaborators (LANL): S. A. Maloy, T. C. Germann, Y. Q. Wang, X. Y. Liu, B. P. Uberuaga, A. F. Voter • 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

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

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

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. Multiplicity of interface atomic structures in FCC-BCC multilayered composites KSmin KS2 (2 interfaces) KS1 Created by simply joining Cu and Nb in the KS OR Interfacial Cu layer has 5% lower atomic density than Cu (111) at 0°K Interfacial Cu atomic layer strained with respect to Cu (111) 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) The interfacial enthalpy of this interface is about 4.5% lower These two interfaces have nearly the same interfacial enthalpies M.J.Demkowicz, J. Wang, R.G. Hoagland, Dislocations in Solids, v.14, p 141, (2008).

7. KS1 Interface defect delocalization leads to radiation resistance Enhanced annihilation probability Low formation energies Change of state 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. Defect formation energies are substantially lower near an interface than in the perfect crystal These properties, together with increased defect mobility at interfaces, favor radiation-induced point defect annihilation at interfaces. M.J. Demkowicz, R.G. Hoagland and J.P. Hirth, Phys. Rev. Lett (2008)

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

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

10. Formulation of quantitative figures of merit to guide further research and bottom-up nanocomposite design Design of composites for radiation tolerance System  W-MgO 4.78 Mo-MgO 2.72 Ag-V 0.9 0.4 Cu-Nb 0.1 Cu-V Pitsch-Petch Fe-Fe3C 0.05 0.04 Fe-W Bagaryatskii Fe-Fe3C 0.01

11. Requirements for a structured research plan Model conditions: In situ probe Ex situ probe Controlled irradiation environment complexity: implanted ions, corrosion, doses, dose rates, 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 Model systems:controlled material complexity Implantation, accelerators, spallation sources, test reactors, CTFs, etc. Compositional: Multi-scale modeling: Directly comparable with model systems and conditions Morphological

12. Summary bottom-up materials design for fusion energy • “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