Intergranular stress-corrosion cracking (IGSCC) is a form of environmentally induced crack propagation causing premature failure of elemental metals and alloys. It is believed to require the ...simultaneous presence of tensile stress and corrosion; however, the exact nature of this synergy has eluded experimental identification. For noble metal alloys such as Ag-Au, IGSCC is a consequence of dealloying corrosion, forming a nanoporous gold layer that is believed to have the ability to transmit cracks into grain boundaries in un-dealloyed parent phase via a pure mechanical process. Here using atomic-scale techniques and statistical characterizations for this alloy system, we show that the separate roles of stress and anodic dissolution can be decoupled and that the apparent synergy exists owing to rapid time-dependent morphology changes at the dealloyed layer/parent phase interface. We discuss the applicability of our findings to the IGSCC of important engineering Fe- and Ni-based alloys in critical applications.
Shear Assisted Processing and Extrusion (ShAPE) -a novel processing route that combines high shear and extrusion conditions- was evaluated as a processing method to densify melt spun magnesium alloy ...(AZ91E) flake materials. This study illustrates the microstructural regimes and transitions in crystallographic texture that occur as a result of applying simultaneous linear and rotational shear during extrusion. Characterization of the flake precursor and extruded tube was performed using scanning and transmission electron microscopy, x-ray diffraction and microindentation techniques. Results show a unique transition in the orientation of basal texture development. Despite the high temperatures involved during processing, uniform grain refinement and material homogenization are observed. These results forecast the ability to implement the ShAPE processing approach for a broader range of materials with novel microstructures and high performance.
The effect of varied thermomechanical processing on discontinuous precipitation (DP) in U–10Mo was investigated, with specific emphasis on understanding the role of grain boundary misorientation in ...DP. Varied prior homogenization heat treatment and thermomechanical processing resulted in differences in both the fraction of DP and the colony width, and was attributed to variations in the grain boundary misorientation distribution. Regardless of the degree of DP-based transformation, extensive growth of DP colonies was dominant on 30°–45° misorientation boundaries. Interestingly, misorientation histograms of the deformed and annealed specimens suggest the processing steps involved may have inhibited DP colony growth along a small fraction of these high angle boundaries. Large-area electron backscatter diffraction montages coupled with high resolution mapping suggest symmetric {110}-type interfaces may be important considerations for mitigating extensive DP growth in this alloy system.
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OBJECTIVE To determine whether interdisciplinary simulation team training can positively affect registered nurse and/or physician perceptions of collaboration in clinical decision making. ...PARTICIPANTS AND METHODS Between March 1 and April 21, 2009, a convenience sample of volunteer nurses and physicians was recruited to undergo simulation training consisting of a team response to 3 clinical scenarios. Participants completed the Collaboration and Satisfaction About Care Decisions (CSACD) survey before training and at 2 weeks and 2 months after training. Differences in CSACD summary scores between the time points were assessed with paired t tests. RESULTS Twenty-eight health care professionals (19 nurses, 9 physicians) underwent simulation training. Nurses were of similar age to physicians (27.3 vs 34.5 years; p =.82), were more likely to be women (95.0% vs 12.5%; p <.001), and were less likely to have undergone prior simulation training (0% vs 37.5%; p =.02). The pretest showed that physicians were more likely to perceive that open communication exists between nurses and physicians ( p =.04) and that both medical and nursing concerns influence the decision-making process ( p =.02). Pretest CSACD analysis revealed that most participants were dissatisfied with the decision-making process. The CSACD summary score showed significant improvement from baseline to 2 weeks (4.2 to 5.1; p <.002), a trend that persisted at 2 months ( p <.002). CONCLUSION Team training using high-fidelity simulation scenarios promoted collaboration between nurses and physicians and enhanced the patient care decision-making process.
Cast stainless steels (CASSs) have been extensively used for the large components of light water reactor (LWR) power plants such as primary coolant piping and pump casing. The thermal embrittlement ...of CASS components is one of the most serious concerns related to the extended-term operation of nuclear power plants. Many past researches have concluded that the formation of Cr-rich
α
′-phase by Spinodal decomposition of
δ
-ferrite phase is the primary mechanism for the thermal embrittlement. Cracking mechanism in the thermally-embrittled duplex stainless steels consists of the formation of cleavage at ferrite and its propagation via separation of ferrite–austenite interphase. This article intends to provide an introductory overview on the thermal aging phenomena in LWR-relevant conditions. Firstly, the thermal aging effect on toughness is discussed in terms of the cause of embrittlement and influential parameters. An approximate analysis of thermal reaction using Arrhenius equation was carried out to scope the aging temperatures for the accelerated aging experiments to simulate the 60 and 80 years of services. Further, an equilibrium precipitation calculation was performed for model CASS alloys using the CALPHAD program, and the results are used to describe the precipitation behaviors in duplex stainless steels. These results are also to be used to guide an on-going research aiming to provide knowledge-based conclusive prediction for the integrity of the CASS components of LWR power plants during the service life extended up to and beyond 60 years.
Electroplating was used as a purification method and produced thick (3.2–12.2 mm) copper deposits of ultra-high radiopurity. Due to the extreme thickness of these electrodeposits compared to ...traditional electroplating, characterization is necessary to prevent costly failures and ensure device reliability. The deposition rate was carefully controlled to maintain a uniform growth front and required plating for a continuous 8 months in order to produce the 12.2-mm-thick copper specimen. Tensile testing shows the electroplated copper to exhibit significant strain hardening as would be expected with face-centered cubic materials, indicating that the material is free of significant defects and voids. Testing of eight tensile samples machined according to ASTM-E8 specifications exhibited yield strengths of 95 ± 4 MPa. Hardness was measured to be 79.8 ± 5.3 HV using a 200-gf load. Microstructure and deformation showed the grains to be highly aligned with respect to the growth direction, and electron backscatter diffraction showed the development of a (110) texture.
The Majorana Demonstrator radioassay program Abgrall, N.; Arnquist, I.J.; Avignone, F.T. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2016, Letnik:
828
Journal Article
Recenzirano
Odprti dostop
The Majorana collaboration is constructing the Majorana Demonstrator at the Sanford Underground Research Facility at the Homestake gold mine, in Lead, SD. The apparatus will use Ge detectors, ...enriched in isotope 76Ge, to demonstrate the feasibility of a large-scale Ge detector experiment to search for neutrinoless double beta decay. The long half-life of this postulated process requires that the apparatus be extremely low in radioactive isotopes whose decays may produce backgrounds to the search. The radioassay program conducted by the collaboration to ensure that the materials comprising the apparatus are sufficiently pure is described. The resulting measurements from gamma-ray counting, neutron activation and mass spectroscopy of the radioactive-isotope contamination for the materials studied for use in the detector are reported. We interpret these numbers in the context of the expected background for the experiment.
We investigated the ambient temperature structural properties (thickness, width, microstructure, and lattice parameter), and the ambient and high temperature (up to 900 K) direct current (DC) ...magnetic properties—saturation magnetization (MS) and intrinsic coercivity (HCI)—of rapidly-solidified (melt-spun) Fe-x wt.% Si (x = 3, 5, & 8) alloys. The wheel surface speeds selected for the study were 30 m/s and 40 m/s. The ribbons produced at the lower wheel surface speed (30 m/s) were continuous having relatively uniform edges compared to the ribbons produced at the higher wheel surface speed. The thickness and the width of the melt-spun ribbons ranged between ∼15 and 60 μm and 500–800 μm, respectively. The x-ray diffraction spectra of the melt-spun ribbons indicated the presence of disordered α-phase, irrespective of the composition, and the wheel surface speed. The lattice parameter decreased gradually as a function of increasing silicon content from ∼0.2862 nm (Fe-3 wt.% Si) to ∼0.2847 nm (Fe-8 wt.% Si). The wheel surface speed showed an insignificant effect on MS while increased silicon content resulted in a decreasing trend in MS. Elevated temperature evaluation of the magnetization (M-T curves at ∼7.96 kA/m) in the case of Fe-3 & 5 wt.% Si alloy ribbons was distinctly different from that of the Fe-8 wt.% Si alloy ribbons. The curves of the as-prepared Fe-3 wt.% Si and Fe-5 wt.% Si alloy ribbons were irreversible while that of Fe-8 wt.% Si was reversible. The MS for any of the combinations of wheel surface speed and composition decreased monotonically with the increase in temperature (from 300 to 900 K). While HCI increased with the increase in temperature for all the wheel surface speed and composition combination, its nature of increase is distinct for Fe-8 wt.% Si alloy ribbons compared to Fe-3 & 5 wt.% Si alloys ribbons. It appears that rapidly-solidified Fe-3 wt.% Si and Fe-5 wt.% Si alloys ribbons are primarily comprised of the α-phase (disordered phase) while the Fe-8 wt.% Si alloy ribbons are comprised primarily of disordered phase along with minor constituents of an ordered phase.
•Structural/magnetic properties of Fe-rich melt-spun Fe-Si alloys were investigated.•Melt-spun ribbons were primarily comprised of disordered α-phase.•Lattice parameter decreased gradually as a function of increasing silicon content.•Saturation magnetization gradually decreased with increase in silicon content.•Saturation magnetization for a composition decreased with increase in temperature.
Shear deformation has been highlighted in multiple research efforts for its ability to impart novel microstructures that demonstrate improvements in mechanical properties. When used to process and ...densify powdered material, these shear-based consolidation techniques are commonly referred to as friction consolidation (FC). In this paper, the microstructural evolution from compacted Cu and Ni powders to a consolidated Cu0.5Ni0.5 alloy is examined. Various stages of porosity reduction and deformation are shown. Deformation was observed to accumulate preferentially in the more ductile material early in the process, leading to the formation of a tortuous microstructural zone. Porosity reduction was extensive, decreasing from ~65% in the pre-compacted state to ~1% in the fully consolidated alloy. The final consolidated alloy showed a ~2× hardness improvement over the unalloyed, compacted material. Unique aspects of this work include demonstration of FC processing to produce an equiaxed, sub-micrometer grain size in samples within a 0.5 to 2 min processing time. The results point to future opportunities to implement shear deformation during powder densification to expand the range of property outcomes in bulk materials.
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•Friction Stir Consolidation (FSC) of Cu and Ni powder was performed.•A tortuous microstructural intermediate zone was observed as porosity decreased.•The intermediate microstructure was caused by shear and pressure gradients.•Shear and pressure gradients generate thermal, chemical and structural zones.•Onset of the intermediate zone coincided with dynamic recrystallization of Cu.•Viscosity differences following Cu recrystallization produced the tortuous zone.
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•Friction consolidation of Cu-Ni powders has revealed unique paths toward alloying.•High shear processing conditions illuminate disparate material properties.•Strength, modulus, and ...hardening variations alter load transfer and alloying pathways.•Infiltration of Cu along Ni-Ni high angle grain boundaries and asymmetric diffusion were observed.
Friction consolidation (FC) is a solid phase processing methodology that densifies a material through high-shear deformation and pressure at elevated temperature. The method has garnered interest in the scientific community because of its ability to produce extremely refined and homogeneous microstructures, off-axis texture development, and improved material properties. This manuscript presents an investigation of Cu and Ni material mixing via evaluation of morphological evolution, grain boundary characterization, and compositional analysis to provide insights on the operational alloying mechanisms occurring under high shear and elevated temperature. Using correlative microscopy techniques, we show alloying progresses via a combination of grain boundary diffusion and interfacial roughening at heterophase boundaries. Evidence supporting Cu infiltration along Ni-Ni grain boundaries along with asymmetric diffusion of Cu into Ni grains is highlighted. The resultant, consolidated microstructure was produced directly from a powder compact in ∼30 s and exhibited a submicrometer, equiaxed grain size.
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