Mechanical response of self-ion irradiated, single crystal, FCC micropillars

Increasing energy demands and regulations on cleaner and more efficient energy sources has reinvigorated research into next generation nuclear reactors. The safe and optimal operation of the various proposed reactors requires the cladding and structural metals to perform under a combination of extreme environments including radiation damage levels \u3e100 dpa. This presentation will highlight a rapid screening technique developed at Sandia National Laboratories to determine the relative merit of implementing various advanced structural alloys and composites in high radiation environments. In addition to an overview of the technique and the wealth of alloy systems it has been applied to, this presentation will focus on the detailed mechanisms that can be elucidated from the micropillar compression of ion irradiated single crystal copper and nickel. Single crystal Cu micropillars self-ion irradiated up to 190 dpa at the end of range were compressed along the \u3c110\u3e to 10% strain. To elucidate the interaction of different length scales on the mechanical response, three specimen configurations were explored: large 10 μm tall, intermediate 5 μm tall, and small 4 μm tall pillars. In a similar manner, pristine and self-ion irradiated \u3c111\u3e Ni pillars were subject to in-situ microcompression in a scanning electron microscope (SEM). By performing these experiments during real time SEM observation a direct correlation between the mechanical responses and the pillars’ structural evolution can be obtained. Specifically, the dynamics resulting from the defect free channel formation and subsequent localization can be associated with heterogeneous plastic flow. This presentation will highlight the multiple length scale effects that are active during the micropillar compression of self-ion irradiated, single crystal, FCC micropillars. These results will be discussed in the context of an end of range effect, a damage gradient effect, and size effects, as well as compared to other small scale mechanical testing methods of ion and neutron irradiated materials. Finally, the benefits and limitations of applying these methods to rapidly screen advanced materials for potential future nuclear reactor applications will be discussed. This study is supported by the Division of Materials Science and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000

Oncogenic Signaling Pathways in The Cancer Genome Atlas

Genetic alterations in signaling pathways that control cell-cycle progression, apoptosis, and cell growth are common hallmarks of cancer, but the extent, mechanisms, and co-occurrence of alterations in these pathways differ between individual tumors and tumor types. Using mutations, copy-number changes, mRNA expression, gene fusions and DNA methylation in 9,125 tumors profiled by The Cancer Genome Atlas (TCGA), we analyzed the mechanisms and patterns of somatic alterations in ten canonical pathways: cell cycle, Hippo, Myc, Notch, Nrf2, PI-3-Kinase/Akt, RTK-RAS, TGFb signaling, p53 and beta-catenin/Wnt. We charted the detailed landscape of pathway alterations in 33 cancer types, stratified into 64 subtypes, and identified patterns of co-occurrence and mutual exclusivity. Eighty-nine percent of tumors had at least one driver alteration in these one alteration potentially targetable by currently available drugs. Thirty percent of tumors had multiple targetable alterations, indicating opportunities for combination therapy

Grain size and particle dispersion effects on the tensile behavior of friction stir welded MA956 oxide dispersion strengthened steel from low to elevated temperatures

The article of record as published may be located at http://dx.doi.org/10.1016/j.msea.2013.09.092This paper shows the dependence of tensile behavior of friction stir welded oxide dispersion strenghtened steel (MA956) on testing temperature and welding parameters. Eight welding conditions were utilized and three produced consolidated defect-free welds in MA956 plate material. Tensile samples were prepared from the welded plate and were subjected to tensile testing with a strain rate of...

Determination of mechanical properties of a MEMS directional sound sensor using a nanoindenter

The article of record as published may be found at https://doi.org/10.1016/j.sna.2012.11.033We use a nanoindenter to measure the stiffness of mechanical components of a microelectromechanical directional sound sensor. The results validate analytical and numerical linear elastic models, identify the physical structures associated with each resonant frequency, and provide an estimate of the maximum sound pressure the sensor can tolerate. Because the sensor has bending and twisting components that act as springs in series, the overall compliance is the sum of several terms, each of which varies with the location of the loading force along the sensor’s surface. By fitting a curve to a plot of the measured overall stiffness vs. location of the loading force, we quantify the separate compliance terms and thereby estimate the resonant frequencies of the corresponding vibrational modes. The frequencies estimated by this method for the two modes are in reasonably good agreement with the measured resonant frequencies. Finally, we establish a minimum failure strength of the sensor, from which we estimate that it can tolerate a sound pressure level greater than about 162 dB without damag

Evolution of Oxide Structures in Friction Stir Welded Alloy MA956

The article of record as published may be found at https://doi.org/10.1017/S1431927615004572Oxide dispersion strengthened alloys are of great potential importance for advanced fission and fusion reactors because of their high temperature strength, creep resistance, and radiation damage resistance.[1] Unfortunately, these materials are not readily joined by fusion welding as the dispersed oxides agglomerate and coarsen in the weld pool, thus drastically reducing the strength of the welded material. Friction stir welding (FSW) can successfully join these materials through a solid-state bonding process, but there is still some reduction in strength due to evolution of the oxide structure.[2] This paper examines the changes in oxide size and phase as a function of FSW parameters in the alloy MA956

Low temperature synthesis of carbon nanotube-reinforced aluminum metal composite powders using cryogenic milling

The article of record as published may be found at http://dx.doi.org/10.1557/jmr.2014.300Carbon nanotube (CNT)-reinforced aluminum composite powders were synthesized by cryogenic milling. The effects of different cryogenic milling parameters and CNT contents on the structural characteristics and mechanical properties of the resulting composite powders were studied. Detailed information on powder morphology and the dispersion and structural integrity of the CNTs is crucial for many powder consolidation methods, particularly cold spray (CS), which is increasingly utilized to produce metal-based nanocomposites. While all of the produced composite powders exhibited particle sizes suitable for spray application, it was found that with increasing CNT content, the average particle size decreased and the size distribution became narrower. The dispersion of CNTs improved with milling time and helped to maintain a small Al grain size during cryogenic milling. Although extensive milling allowed for substantial grain size reduction, the process caused notable CNT degradation, leading to a deterioration of the mechanical properties of the composite

Impact of Friction Stir Welding on the Microstructure and Microtexture of Ferritic-Martensitic HT9 Steel

The article of record as published may be found at https://doi.org/10.1017/S1431927613005709Ferritic-martensitic steels are a key material class for structural components in both fission and fusion reactors. Joining components using fusion welding; however, can create problems including material softening, residual stresses, porosity, etc. Friction stir welding (FSW) has been shown as an effective joining mechanism for a host of engineering materials including, more recently, some steels.[1] The processing-microstructure relationships for high chromium, ferritic-martensitic steels have not yet been established. In particular, the effect of varying FSW parameters on the evolution of microstructure has not been addressed. In this research, electron backscatter diffraction (EBSD) and optical microscopy were used to characterize the impact of FSW upon the microstructure of a modified HT9 steel for three different welding conditions of increasing heat input