Hydrogen embrittlement susceptibility and permeability of two ultra-high strength steels

Slow displacement rate tensile tests were carried out in a saturated H₂S solution to investigate the effect of hydrogen embrittlement on notched tensile strength (NTS) and fracture characteristics of two ultra-high strength steels (PH 13-8 Mo stainless steel and T-200 maraging steel). Hydrogen permeation properties were determined by an electrochemical permeation method. The results of permeation tests indicated that over-aged specimens showed a lower diffusivity/hydrogen flux and higher solubility than those solution-annealed. The great increase in reverted austenite (irreversible hydrogen traps) together with numerous precipitates at the expense of dislocations (reversible) in the over-aged specimen led to such a change in permeability. Ordinary tensile tests indicated that four tested specimens had roughly the same yield strength level. Hence, the hydrogen embrittlement susceptibility of the material could be related to their permeation properties. The uniform distribution of strong hydrogen traps in over-aged specimens instead of weak traps in the solution-annealed impeded the hydrogen transport toward the strained region, thus, the resistance to sulfide stress corrosion cracking was improved in over-aged specimens.     

Using Difference‐Based Methods for Inference in Regression with Fractionally Integrated Processes

Abstract. This paper suggests a difference‐based method for inference in the regression model involving fractionally integrated processes. Under suitable regularity conditions, our method can effectively deal with the inference problems associated with the regression model consisting of nonstationary, stationary and intermediate memory regressors, simultaneously. Although the difference‐based method provides a very flexible modelling framework for empirical studies, the implementation of this method is extremely easy, because it completely avoids the difficult problems of choosing a kernel function, a bandwidth parameter, or an autoregressive lag length for the long‐run variance estimation. The asymptotic local power of our method is investigated with a sequence of local data‐generating processes (DGP) in what Davidson and MacKinnon [Canadian Journal of Economics. (1985) Vol. 18, pp. 38–57] call ‘regression direction’. The simulation results indicate that the size control of our method is excellent even when the sample size is only 100, and the pattern of power performance is highly consistent with the theoretical finding from the asymptotic local power analysis conducted in this paper.     

Fatigue crack growth behavior of laser-processed 304 stainless steel in air and gaseous hydrogen

Fatigue crack growth test was performed to evaluate fatigue behavior of 304 stainless steel specimens with or without laser processing (welding and surface treatment) in air and gaseous hydrogen. As the crack propagation normal to the laser welding or scan direction, the laser-processed specimens exhibited a higher resistance to crack growth in the low stress intensity factor range (ΔK) than the as-received steel plates regardless of testing environments. However, the marked retardation of crack growth behavior vanished for welded specimens subjected to a 850 °C/h stress relief treatment or with a shorter distance from notch tip to the weld centerline in the test.Fatigue-fractured appearance of the steel plate tested in air was composed of mainly transgranular fatigue fracture and some flat facets, along with a small amount of intergranular fracture. While quasi-cleavage fracture and few twin boundary separations were observed for the same specimen in hydrogen. On the other hand, the lower crack growth rate of laser-processed specimens in both air and hydrogen was accompanied with rubbed areas on the fracture surfaces. It was found that the extent of quasi-cleavage fracture was related to the formation of strain-induced martensite, which would contribute to an increased fatigue crack growth rate of all specimens in gaseous hydrogen.     

CHL1 encodes a component of the low-affinity nitrate uptake system in Arabidopsis and shows cell type-specific expression in roots

The Arabidopsis CHL1 (AtNRT1) gene confers sensitivity to the herbicide chlorate and encodes a nitrate-regulated nitrate transporter. However, how CHL1 participates in nitrate uptake in plants is not yet clear. In this study, we examined the in vivo function of CHL1 with in vivo uptake measurements and in situ hybridization experiments. Under most conditions tested, the amount of nitrate uptake by a chl1 deletion mutant was found to be significantly less than that of the wild type. This uptake deficiency was reversed when a CHL1 cDNA clone driven by the cauliflower mosaic virus 35S promoter was expressed in transgenic chl1 plants. Furthermore, tissue-specific expression patterns showed that near the root tip, CHL1 mRNA is found primarily in the epidermis, but further from the root tip, the mRNA is found in the cortex or endodermis. These results are consistent with the involvement of CHL1 in nitrate uptake at different stages of root cell development. A functional analysis in Xenopus oocytes indicated that CHL1 is a low-affinity nitrate transporter with a K(m) value of approximately 8.5 mM for nitrate. This finding is consistent with the chlorate resistance phenotype of chl1 mutants. However, these results do not fit the current model of a single, constitutive component for the low-affinity uptake system. To reconcile this discrepancy and the complex uptake behavior observed, we propose a "two-gene" model for the low-affinity nitrate uptake system of Arabidopsis.     

Characterization of low-light-level cameras for digitized video microscopy

The use of low-light-level video cameras and solid-state image detectors in conjunction with image digitizers for optical microscopy is increasing dramatically as more people learn about such systems, and as they become more powerful, less expensive, and easier to use. However, there is currently little information available allowing comparison between cameras, or for determining camera suitability for a given experiment. In this paper, we describe a series of tests designed to characterize the performance of low-light-level cameras. The results of these tests should assist in the selection of appropriate cameras for given video microscopy applications.     

Lift-off and re-growth of ZnSSe epilayer

We try to study the epitaxial ZnSe re-growth on lift-off ZnSSe epilayer. First, the ZnSSe lift-off technique from ZnSSe/GaAs substrate was investigated. The ZnSSe/GaAs wafer was glued on an indium/glass substrate and an etching solution of NH₄OH (30%):H₂O₂ (30%)=9:1 was used for the lift-off of ZnSSe epilayer. From photoluminescence examination, the intensities of the near-band and broad-band emission of ZnSSe epilayer increased from the reflection of In mirror after the lift-off. Re-growth of ZnSSe epilayers on ZnSSe/indium/glass substrate at 220°C was studied by metalorganic vapor-phase epitaxy. The near-band emission is stronger and the broad-band emission decreases after re-growth. It shows a near-band emission emission at 438 nm with an FWHM of 26.8 meV at 77 K. It means that a high-quality re-grown ZnSe epilayer can be obtained.     

Mathematical model and tooth surfaces of recess action worm gears with double-depth teeth

In this study, the surface equations of recess action (RA) worm gears with double-depth teeth, generated by a ZN worm-type hob cutter, are proposed. Based on the generation mechanism and the theory of gearing, a mathematical model of a series of worm gears, semi RA, full RA and standard proportional tooth types, with double-depth teeth is developed as the function of design parameters of the ZN worm-type hob cutter. According to the derived tooth surface equations, computer graphs of a series of worm gears with double-depth teeth are plotted. Tooth surface variations of the generated RA worm gears due to the varying pitch line, pressure angle and tooth height of the hob cutter are also investigated.     

Removing tool marks of blade surfaces by smoothing five-axis point milling cutter paths

Focused on the reverse movements of moving axes along five-axis tool paths, this study presents a procedure of removing a gouge phenomenon on impeller surfaces in five-axis machining. That is, when an impeller of a centrifugal compressor is being cut in finish milling, reverse movements and/or other linearization problems of moving axes along a five-axis interference-free tool path may make a cutter leave tool marks on the impeller surfaces. For generating interference-free cutter location (CL) data needed in rough, semi-finish and finish five-axis cutting processes, first, a simple yet useful approach is proposed. To identify the potential gouge area and to solve the problem for a tool path having reverse motion directions with its moving axes in finish milling, the CL data are further smoothed to remove the reverse movements about its rotating and tilting axes. The effectiveness of this procedure has been experimentally confirmed by successful five-axis finish milling of an impeller without leaving tool marks on its surfaces. In addition, with the spline tool paths, the machining time can be saved up to 23.57%.     

Synthesis and properties of polyimide (containing naphthalene) nanocomposites with organo‐modified montmorillonites

2,7‐Bis(4‐aminophenoxy) naphthalene (BAPN), a naphthalene‐containing diamine, was synthesized and polymerized with a 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) to obtain a polyimide (PI) via thermal imidization. To enhance the thermal and mechanical properties of the polymer, PI–Montmorillonite (MMT) nanocomposites were prepared from a DMAc solution of poly(amic acid) and a DMAc dispersion of MMT, which were organo‐modified with various amounts of n‐dodecylamine (DOA) or cetylpyridium chloride (CPC). FTIR, XRD, and TEM (transmission electron microscopy) were used to verify the incorporation of the modifying agents into the clay structure and the intercalation of the organoclay into the PI matrix. Results demonstrated that the introduction of a small amount of MMT (up to 5%) led to the improvement in thermal stability and mechanical properties of PI. The decomposition temperature of 5% weight loss (T_d,5%) in N₂ was increased by 46 and 36°C in comparison with pristine PI for the organoclay content of 5% with DOA and CPC, respectively. The nanocomposites were simultaneously strengthened and toughened. The dielectric constant, CTE, and water absorption were decreased. However, at higher organoclay contents (5–10%), these properties were reduced because the organoclay was poorly dispersed and resulted in aggregate formation. The effects of different organo‐modifiers on the properties of PI–MMT nanocomposite were also studied; the results showed that DOA was comparable with CPC. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Enhanced microwave absorption of La0.7Sr0.3MnO3−δ based composites with added carbon black

Composites consisting of carbon black (CB) particles, La_0.7Sr_0.3MnO_3−δ (LSMO) powder, and epoxy resin were prepared for development of a high performance microwave absorber. This study investigated the influence of adding amounts of LSMO powder (60, 70, and 80 wt%) on complex permittivity, complex permeability, and reflection loss for CB (5 wt%)-epoxy composites. The variation of complex permittivity and complex permeability with frequency of the composites was measured by the cavity perturbation technique in the range of 7–14 GHz. It was found that the real part of the complex permittivity increased with increasing LSMO addition and the imaginary part of the complex permeability decreased with increasing frequency. The microwave absorption results indicated that the composite filled with 5 wt% CB particles and 80 wt% LSMO powder had the best absorption performance. The maximum reflection loss was −23.63 dB at 7.87 GHz and the absorbing bandwidth at −10 dB was 1.75 GHz with a matching thickness of 5 mm.