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Research Papers

Design of Radiation Tolerant Nanostructured Metallic Multilayers

[+] Author and Article Information
X. Zhang1

 Department of Mechanical Engineering, Materials Science and Engineering Program, Texas A&M University, College Station, TX 77843-3123zhangx@tamu.edu

E. G. Fu, Nan Li, A. Misra, Y.-Q. Wang

Materials Physics and Application Division, Los Alamos National Laboratory, Los Alamos, NM 87545

L. Shao

 Department of Nuclear Engineering, Texas A&M University, College Station, TX 77843-3128

H. Wang

 Department of Electrical Engineering, Texas A&M University, College Station, TX 77843-3128

1

Corresponding author.

J. Eng. Mater. Technol 134(4), 041010 (Aug 24, 2012) (9 pages) doi:10.1115/1.4006979 History: Received December 09, 2011; Revised April 23, 2012; Published August 24, 2012; Online August 24, 2012

We review He ion induced radiation damage in several metallic multilayer systems, including Cu/V, Cu/Mo, Fe/W, and Al/Nb up to a peak dose of several displacements per atom (dpa). Size dependent radiation damage is observed in all systems. Nanolayer composites can store a very high concentration of He. Layer interfaces promote the recombination of opposite type of point defects and hence reduce the accumulative defect density, swelling, and lattice distortion. Interfaces also alleviate radiation hardening substantially. The chemical stability of interfaces is an important issue when considering the design of radiation tolerant nanolayer composites. Immiscible and certain miscible systems possess superior stability against He ion irradiation. Challenge and future directions are briefly discussed.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

XTEM micrograph of (a) as-deposited and (b) He ion irradiated Cu/V 2.5 nm multilayers. The as-deposited films have K-S orientation relationship: Cu {1 1 1}//V {1 1 0}//interface and Cu ⟨1 1 0⟩//V ⟨1 1 1⟩. He bubbles were observed in irradiated films and the radiation damage peaked at ∼200 nm from surface (with a maximum peak He concentration of ∼4–5 at. %) as predicted from SRIM simulations. There is insignificant texture evolution as revealed by SAD patterns.

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Figure 2

Comparison of STEM micrograph of irradiated Cu/V 2.5 nm multilayers. (a) At a region ∼1000 nm away from surface, there is little or no damage in this region. (b) A region of peak damage shows the retention of clear layer interface. (c) EDX chemical analysis of the same specimen along the interface normal direction across three regions (the close-to-surface, peak damage, and no damage region) clearly reveal chemically modulated composition of multilayer films in all three regions. Hence, it again confirms that interface remains stable after radiation.

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Figure 3

(a) XTEM of as-deposited Fe/W 1 nm multilayer shows distinct layer interfaces and columnar grains. (b) HRTEM micrograph of the same specimen reveals the formation of semicoherent interfaces. Misfit dislocations are identified along interfaces. (c) He ion irradiation at the peak damage zone shows the destruction of layer interface.

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Figure 4

Underfocused XTEM micrographs reveal the retention of interfaces in He ion irradiated Al/Nb 2.5 nm multilayer at (a) surface, (b) peak damage, and (c) little radiated or unirradiated regions. He bubbles of low density are observed in the peak damage region (b). Figures (a′)–(c′) are HRTEM micrographs of the corresponding regions. (a′) Interfaces appear rough close to film surface. (b′) Intermixing may have occurred at the interfaces, however, the majority of Nb and Al layers are clearly distinguishable. (c′) Interfaces are intact in region of little or no radiation damage.

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Figure 5

STEM micrographs of He ion irradiated Al/Nb 2.5 nm multilayers at (a) surface, (b) peak damage, and (c) unirradiated region. Distinctive layer interfaces are clearly resolved in all regions. Figures (a′)–(c′) show the corresponding composition analyses along line markers. Modulated composition profiles are revealed in (a′) and (c′). But intermixing clearly occurs in region (b′).

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Figure 6

Depth dependent distribution of He bubble density in He irradiated pure Cu films (shown by horizontal dash line), Cu/V 50 nm (solid squares), and Cu/V 2.5 nm multilayers. The peak bubble density occurs at a depth similar to that of maximum He concentration. The maximum bubble density in Cu/V 50 nm film is three times that of Cu/V 2.5 nm films but is still lower than that in pure Cu films.

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Figure 7

SRIM simulations of depth dependent He concentration in irradiated Cu/V 5 and 50 nm films. The horizontal solid and dashed lines show the threshold He concentration to detect bubbles (obtained from XTEM studies) in irradiated Cu/V 2.5 nm and Cu/V 50 nm films to be ∼1 at. % and 0.28 at. %, respectively. SRIM was performed for Cu/V 5 nm instead of Cu/V 2.5 nm film due to the depth limitation of the code.

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Figure 8

(a) The He (solid curve) and vacancy concentration (dashed curve) profiles of He irradiated Cu/Mo 5 nm films obtained from SRIM simulations. Arrows indicate the location of specimens examined by XTEM experiments in (b)–(f). Note that locations (c) and (f) have the same He concentration, but the vacancy concentration at (c) is a lot greater. He bubbles are observed mainly in Cu at location b (b), begin to appear in Mo in region c (c), and start to grow primarily in Cu at location d (d) with arrows pointing at larger bubbles along layer interfaces. Bubbles are distributed throughout the layers in (e), and predominantly aligned along interface in (f).

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Figure 9

(a) Depth profile of lattice distortion of irradiated Cu/V 2.5 nm and Cu/V 50 nm films. Peak damage occurs in both systems at a depth comparable to peak He concentration. The magnitude of peak distortion is three times lower in Cu/V 2.5 nm than the Cu/V 50 nm films. (b) Similar plot for He ion irradiated Fe/W 50 nm films. Peak distortion of Fe occurs at a similar depth to the maximum of superimposed He concentration profile. However, the maximum distortion of W takes place at a greater depth.

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Figure 10

Radiation hardening of several He ion irradiated multilayer systems. (a) Radiation hardening in Cu/V shows clear size dependence: suppression of radiation hardening by decreasing layer thickness. At greater h, radiation hardening approaches that of single layer Cu and V films. (b) A similar size dependent radiation hardening is observed in Fe/W multilayers. (c) An opposite size dependent radiation hardening is observed in Al/Nb. The enhanced hardening is attributed to the formation of a hard Nb3 Al layer. The calculated hardening shown by two dash lines indicates that Nb3 Al is ∼0.5 nm in thickness.

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