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. Demkowicz1

A. Misra2, R. G. Hoagland3, M. Nastasi2

2MPA-CINT: Center for Integrated Nanotechnologies3MST-8: Structure-Property Relations

Los Alamos National LaboratoryLos Alamos, NM 87545

1Department of Materials Science and EngineeringMassachusetts 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

Priorities, Gaps and OpportunitiesPriorities, Gaps and Opportunitiesin materials research for fusion energyin materials research for fusion energy

Priorities, Gaps and OpportunitiesPriorities, Gaps and Opportunitiesin materials research for fusion energyin 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)

Nanocomposites for nuclear fusionNanocomposites for nuclear fusionNanocomposites for nuclear fusionNanocomposites 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

Nanocomposites for nuclear fusionNanocomposites for nuclear fusionNanocomposites for nuclear fusionNanocomposites 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

The need for bottom-up materials designThe need for bottom-up materials designThe need for bottom-up materials designThe 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

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

KS1 KS2

(2 interfaces)

KSmin

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 structuresMultiplicity of interface atomic structuresin FCC-BCC multilayered compositesin FCC-BCC multilayered composites

Multiplicity of interface atomic structuresMultiplicity of interface atomic structuresin FCC-BCC multilayered compositesin FCC-BCC multilayered composites

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

KS1

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.

KS1 + vac→ KS2KS2 +SIA→ KS1

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 Interface defect delocalization leads to radiation resistanceradiation resistance

Interface defect delocalization leads to Interface defect delocalization leads to radiation resistanceradiation resistance

Relating interface structure to defect propertiesRelating interface structure to defect propertiesabundance of delocalization sitesabundance of delocalization sites

Relating interface structure to defect propertiesRelating interface structure to defect propertiesabundance of delocalization sitesabundance of delocalization sites

Relating interface structure to defect propertiesRelating interface structure to defect propertiesenergies of defect delocalizationenergies of defect delocalization

Relating interface structure to defect propertiesRelating interface structure to defect propertiesenergies of defect delocalizationenergies of defect delocalization

Design of composites for radiation tolerance

Ag-V

Cu-NbCu-VPitsch-PetchFe-Fe3C

Fe-WBagaryatskiiFe-Fe3C

0.90.40.1

0.05

0.04

0.01

System

Mo-MgO2.72

W-MgO4.78

Formulation of quantitative figures of meritFormulation of quantitative figures of meritto guide further research and to guide further research and bottom-up bottom-up nanocomposite designnanocomposite design

Formulation of quantitative figures of meritFormulation of quantitative figures of meritto guide further research and to guide further research and bottom-up bottom-up nanocomposite designnanocomposite design

Compositional:

Morphological

Model systems: controlled material

complexity

Model conditions:In situ probe Ex 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 planRequirements for a structured research planRequirements for a structured research planRequirements for a structured research plan

• “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

SummarySummarybottom-up materials design for fusion energybottom-up materials design for fusion energy

SummarySummarybottom-up materials design for fusion energybottom-up materials design for fusion energy