Mary Ann Hill

Mechanical stability and electrical conductivity of Cu-Ag filamentary microcomposites

Abstract One of the most important features in two-phase Cu–Ag filamentary microcomposites is the abundance of interfaces compared with conventional copper-based alloys. In heavily drawn Cu–Ag filamentary microcomposites, the microstructure is extremely fine and the interphase area is too large to maintain a stable internal dislocation structure because of closely spaced filaments. Rather, most dislocations are thought to be absorbed at the interfaces as the draw ratio increases. The mechanical and electrical properties of Cu–Ag filamentary microcomposite wires were examined and correlated with the microstructural changes caused by thermomechanical treatments. The study of the electrical conductivity combined with the microstructural analyses indicates that the resistivity of Cu–Ag microcomposites is predominantly controlled by electron scattering at Cu–Ag interfaces. The substantial increase in electrical conductivity at high annealing temperatures is mainly due to dissolution and coarsening of silver filaments. The relatively low ratio of the resistivities at 293 and 77 K (ρ293 K/ρ77 K) can also be explained by the contribution of interface scattering.

Microstructural stability of Cu–Nb microcomposite wires fabricated by the bundling and drawing process

Abstract The microstructural stability of Cu–Nb microcomposite wires fabricated by the bundling and drawing process was examined using TEM (Transmission Electron Microscopy). No flaws were observed near the interface regions between the bundled wires and the copper can, suggesting excellent bonding. Nb filaments were randomly distributed throughout the copper matrix and appeared straight or slightly curved in the bundled wires. The absence of heavily kinked filaments in the bundled wires is attributed to the break-up and cylinderization of niobium filaments during the bundling process. Niobium filaments were dissolved and numerous niobium precipitates formed in the copper matrix during high temperature bundling process. Twin bands were observed in the Cu–Nb, with the Nb filaments acting as barriers to twin propagation. Occasionally, the copper matrix on either side of the Nb filaments was found to have different texture components, which is thought to result from the reorientation of [111] into near [200] by twinning.

Assessment of Corrosion-Based Failure in Stainless Steel Containers Used for the Long-Term Storage of Plutonium-Based Salts

Abstract This paper summarizes our efforts to assess corrosion-related failure in stainless steel long-term storage containers bearing plutonium oxides and electrorefining salts. Pitting corrosion of the internal can wall is believed to occur when these salt particles deliquesce forming the electrolyte necessary for corrosion-electrochemistry. Extrapolation of pit depths from coupon studies using generalized extreme value (GEV) statistics found that the probability of a through-wall corrosion pit is finite; the maximum pit depth after 50 years would be on the order of 1.7 mm where the container wall is only 1.6 mm thick. To assess susceptibility to environmental cracking fracture toughness (J1C), experiments were used in conjunction with a J-integral diagram constructed using the GE/EPRI method for linear elastic-plastic materials. As apart of this analysis, the residual stress associated with the weld was measured using the laser contour method. The hoop stress in the weld region was found to be on the o...

Influence of Preoxidation on the Corrosion of Steels in Liquid Lead-Bismuth Eutectic

Abstract Oxidation studies of martensitic/ferritic and austenitic steels have been conducted in static lead bismuth eutectic (LBE). Samples were preoxidized in an air/H2O gas mixture prior to immersion in LBE. Preoxidation films grown on HT-9 at 800°C for 48 h had a bilayer structure, an outer Fe-rich layer, and an inner Cr-rich layer. Glancing angle x-ray diffraction data found that two distinct structures were present in this oxide: Fe1+xCr2−xO4 spinel (cubic, face-centered cubic [fcc]) and (Cr,Fe)2O3 (rhombohedral, corundum). Magnetite formation (Fe3O4) was ruled out. Immersion in LBE resulted in the growth of an Fe-rich film on top of the preoxidation layer. It was concluded that the growth mechanism was Fe+++ interstitial transport from the metal/oxide interface. Preoxidized films grown on Type 316 (UNS S31600) stainless steel (SS) at 800°C for 64 h resulted in a Cr-rich inner layer and Fe-rich outer layer. X-ray diffraction found both Fe1+xCr2−xO4 spinel (cubic) and (Cr,Fe)2O3 corundum (rhombohedral...

Influence of Beryllides on the Corrosion of Commercial Grades of Beryllium

Abstract The bulk form of the Be intermetallics FeAlBe4, FeBe5, and TiBe12 were examined in solutions ranging in pH from 2 to 12.5 at ambient temperature. The intermetallics were manufactured by ar...

Preparation of B4C/Al composites for image analysis

Abstract Composites made by infiltrating B 4 C networks with aluminum, or its alloys, are of interest for lightweight armor applications. Image analysis plays an important part in correlating the microstructures of such composites with their mechanical properties. Accurate image analysis requires a high degree of perfection in the metallographic preparation, which is particularly difficult where the phases present have such disparate hardnesses and reactivities. Two preparation procedures have been developed that produce adequate contrast and definition for analysis of key microstructural features.

Cameco UO3 Materials Analysis

Uranium trioxide (UO{sub 3}) was characterized using a variety of techniques to better understand its physical properties. Scanning electron microscope (SEM) images were collected to examine particle morphology, which consisted of semi-spherical particles that tended to agglomerate before sonication. Particle size analysis revealed a singular mode distribution with a mean particle size of 43.0 {micro}m. After sonication a bimodal distribution was produced with peak particle sizes at 0.226 {micro}m and 9.43 {micro}m. The O/U ratio was measured to be 3.09 by Cameco in 2009, by gravimetric analysis. X-ray diffraction (XRD) showed that the sample was mostly {gamma}-UO{sub 3} (87.1%) with a small amount of UO{sub 3} {center_dot} 0.80 H{sub 2}O (12.9%). Bulk and tap densities were determined to be 3.678 {+-} 0.2 and 4.81 {+-} 0.2 g/cm{sup 3}, respectively (crystalline density is 7.3 g/cm{sup 3}). The stoichiometry was measured to be 2.99 in 2012.