Design of composite materials for outgassing of implanted He M. J. - PowerPoint PPT Presentation

Design of composite materials 
 for outgassing of implanted He M. J. Demkowicz MIT Department of Materials Science and Engineering, Cambridge, MA 02139 Sponsors: Acknowledgements: • CMIME, an Energy Frontier Research A. Kashinath, D. Yuryev, Center funded by DOE, Office of Science P. Wang, J. Majewski, A. Misra, under Award Number 2008LANL1026 X. Zhang, D. Bhattacharyya, … ICTP-IAEA 2014 • LANL LDRD program Trieste, Italy

He-induced damage He-implanted W, T=1000-2000K S. Kajita et al. , Nucl. Fus. 49 , 095005 (2009) Can we design a materials where this sort of damage does not occur?

Channels for continuous He outgassing Cu-Nb layered composites Free surface Incident He Nb Cu No design: uncontrolled precipitation Free surface Incident He Design: channels for He outgassing W. Z. Han et al. , J. Nucl. Mater. 452 , 57 (2014) D. V. Yuryev et al. , APL under review (2014)

Outline • Modeling He precipitation in metal multilayers • Experimental validation of modeling results • Design of metal composites for He outgassing

Misfit dislocation patterns at Cu-Nb interfaces All Cu‐Nb interfaces in magnetron spu6ered composites have the same crystallography: {111} fcc || {110} bcc and <110> fcc || <111> bcc <112> <110> <111> Cu Nb <110> <112> <111>

He trapping at Cu-Nb interfaces is quasi-static • 35 keV He ions are implanted to ()*+$&,$,-.& ! a dose of 10 17 /cm 2 in 3 hours => 12 ! 1 He atom reaches the vicinity of a trap every ~12 minutes 4-5526-.& ! • He migration energy at the 78$**-&9 ! interface is ~0.1 eV => time to find the trap <1ns (&,"85$%" ! • Vacancy migration energy at the /0 ! interface is ~0.4 eV => time to equilibrate vacancy concentration <1s !" ! #$%$&%' ! 34( ! Trap [1] A. Y. Dunn et al, JNM 435 141 (2013); [2] K. Kolluri et al , PRB 84 , 104102 (2011)

Atomic-level modeling of He trapping 
 at a Cu-Nb interface using a custom-made EAM potential Iterative method for Outcome: He clusters introducing He into interface: grow at MDIs on Cu side of interface Equilibrium He cluster • There is a thermodynamic Remove Cu or Nb Insert He into driving force for clusters to atoms until no lowest energy coalesce, but the kinetics of negative vacancy location coalescence is very slow. energy sites remain • He/vacancy ratio ≈ 1 A. Kashinath et al. , PRL 110 , 086101 (2013)

Two modes of He cluster growth (c) 20 He (b) 15 He (a) 10 He (d) 40 He (e) 80 He - He - Cu - Nb Along the interface Normal to the interface, into Cu layer A. Kashinath et al. , PRL 110 , 086101 (2013)

Mechanism of interfacial He precipitation: 
 wetting at misfit dislocation intersections Wetting Coefficient : Cu W = γ Cu-Nb + γ He-Cu – γ He-Nb Nb 0.8 80 0.75 W<0 A) < 112 > Cu || < 112 > N b ( ˚ 0.7 60 0.65 “ Heliophobic ” Wetting Non-wetting W > 0 W < 0 0.6 W<0 40 0.55 Interface Energy (J/m 2 ) 0.5 γ He-Cu 1.93 20 γ He-Nb 2.40 0.45 “Heliophilic” γ Cu-Nb Depends on location in 0.4 the interface plane J/m 2 0 20 40 60 80 < 110 > Cu || < 111 > N b ( ˚ A)

Outline • Modeling He precipitation in metal multilayers • Experimental validation of modeling results • Design of metal composites for He outgassing

Critical He concentration to observe bubbles Scales with interface area/vol. Depends on interface type: – Cu-Nb: 8.5 atoms/nm 2 – Cu-Mo: 3.0 atoms/nm 2 – Cu-V: 1.9 atoms/nm 2 M. J. Demkowicz et al. , Appl. Phys. Lett. 97 , 161903 (2010)

Agreement between model, TEM, and NR o b Areal density, ρ , of M V N - - - u u u C C C heliophilic patches in 0.006 0.385 O − lattice TEM Cu‐Nb 0.005 0.125 NR critical He concentration (#/ ˚ A 2 ) 0.315 Areal density of MDIs (#/ ˚ reduced critical dose (#/ ˚ 0.004 0.1 0.245 " 0.003 0.075 Cu‐V 0.175 0.002 0.05 0.105 " A 2 ) A 2 ) 0.001 0.025 0.035 ! 0 0.8 0.85 0.9 0.95 a bcc / a f cc Kurdjumov-Sachs orientation relation, closest-packed interface planes A. Kashinath et al. , JAP 114 , 043505 (2013)

Outline • Modeling He precipitation in metal multilayers • Experimental validation of modeling results • Design of metal composites for He outgassing

Designing interfaces that outgas He Model 2: Model 2: wetting of misfit quantized Frank-Bilby equation dislocation intersections + anisotropic elasticity Interface composition Misfit dislocation intersections Precipitation of linear and crystallography (MDIs) closely spaced in one He channels with MDI direction and far apart in the pattern as a template perpendicular direction θ l min l � FCC, a FCC , {111} BCC, a bcc , {110} D. V. Yuryev and M. J. Demkowicz, APL under review (2014)

Two degrees of freedom: θ and ρ θ FCC, a fcc , {111} ρ =a bcc /a fcc BCC, a bcc , {110} D. V. Yuryev and M. J. Demkowicz, APL under review (2014)

Design criteria Criterion 1: Criterion 2: l min lower < l � < l � cut upper l min < l min l � l � lower l � • Precipitates overlap along l min : channels sufficiently far prior to bubble-to-void transition apart not to overlap upper l � • : channels sufficiently close to getter He before it clusters l min l � (multiples of a fcc ) (multiples of a fcc ) ρ=a bcc /a fcc D. V. Yuryev and M. J. Demkowicz, APL under review (2014)

upper l � f bind < 10 � 2 T‐t l envelopes where for Rate theory model for He clustering K 0 =10 32 /m 2 s and different values of l � t l upper l � 5 4 K i a fcc f bind = R max = 10 � 2 = l � < f bind K i 6 D He upper = 30 We chose: l �

Solution space ρ=a bcc /a fcc Cu‐V Pt‐Nb, Pt‐Ta Pd‐Fe D. V. Yuryev and M. J. Demkowicz, APL under review (2014) Sputter deposited CuV interfaces are good candidates for He outgassing

Designing interfaces that outgas He g n i l e d o m heliophobic e l a c s heliophilic i t l u m : m e b l o r p d r a w r o F ROM1: He clusters interface wetting <112> <110> Cu <111> Atomic- Nb level insight: precipitation mechanism Cu Phase‐field Model system: n model g i s e Nb d reliable simulation l a n o i t a t u p m <110> o c : m AnalyRcal e <112> l b o r p <111> e model s r e v n I Templated He precipitation: enables outgassing We6able ROM 2: regions designer interface dislocation arrangement He resistant interface: could not have been We are here found by “hit-or-miss”

Conclusions • He precipitates on misfit dislocation intersections (MDIs) at interfaces in fcc/bcc metal layered composites • Precipitation occurs by wetting of high energy regions of the interface, which are located at MDIs • Layered composites containing interfaces that template He precipitation into continuous channels have been designed and are now being synthesized and tested • Such composites may mitigate He-induced surface damage by providing paths for He outgassing while maintaining cohesion across the interface