Design of Nano-Composites for Ultra-High Strengths and Radiation Damage Tolerance
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1188-LL06-01
Design of Nano-Composites for Ultra-High Strengths and Radiation Damage Tolerance A. Misra1, X. Zhang2, M.J. Demkowicz3, R. G. Hoagland1 and M. Nastasi1, 1 Los Alamos National Laboratory, MS K771, Los Alamos, NM 87545. 2 Texas A&M University, College Station, TX. 3 MIT, Cambridge, MA. ABSTRACT The combination of high strength and high radiation damage tolerance in nanolaminate composites can be achieved when the individual layers in these composites are only a few nanometers thick and therefore these materials contain a large volume fraction associated with interfaces. These interfaces act both as obstacles to slip, as well as sinks for radiation-induced defects. The morphological and phase stabilities of these nano-composites under ion irradiation are explored as a function of layer thickness, temperature and interface structure. Using results on model systems such as Cu-Nb, we highlight the critical role of the atomic structure of the incoherent interfaces that exhibit multiple states with nearly degenerate energies in acting as sinks for radiation-induced point defects. Reduced radiation damage also leads to a reduction in the irradiation hardening, particularly at layer thickness of approximately 5 nm and below. The strategies for design of radiation-tolerant structural materials based on the knowledge gained from this work will be discussed. KEYWORDS: Irradiation damage, dislocations, multilayers, interfaces INTRODUCTION The performance of structural materials in extreme environments of irradiation and temperature must be significantly improved to extend the reliability, lifetime, and efficiency of future nuclear reactors [1]. In reactor environments, damage introduced in the form of radiationinduced defects and helium results in embrittlement and dimensional instability. Therefore, the ability to control radiation-induced point defects and helium bubble nucleation and growth is a crucial first step to improving the mechanical properties of irradiated metals. This calls for novel approaches in designing structural materials that resist radiation damage while maintaining high strength and toughness. Using nanolayered metallic composites as model systems, we highlight how tailoring the length scales (layer thickness) and interface properties can provide insight into ways of designing radiation damage tolerant structural materials. The experiments described here were conducted on sputter deposited Cu-Nb multilayers and single layer Cu and Nb samples using He+ ion implantation to cover a broad range of irradiation conditions and layer thicknesses as described below [2-5] (throughout this article, multilayers are designated by the individual layer thickness or one-half of the bilayer period. Thus, 2 nm multilayer refers to a sample with a bilayer period of 4 nm with 2 nm Cu and 2 nm Nb layers). Cu and Nb have a positive heat of mixing, very limited solid solubility, and no tendency to from intermetallic compounds. Thus, the interfaces between Cu and Nb layers are very distinct with little evidence of m
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