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To improve the superplasticity of Inconel 718, cold rolling with 84% reduction, followed by two-stage annealing, was designed to refine and homogenize the grains. Compared with cold rolling and single-stage annealing, a finer grain size of 1.21 μm was obtained and provided better superplasticity (up to 657% elongation) at 950 °C with a strain rate range of 6 × 10-4 to 1 × 10-2 s-1. Sizeable plastic deformation introduces plenty of crystal defects and storage energy, which contributes to the dense and fine distribution of δ phase in the first stage annealing and enhances the driving force for static recrystallization (SRX) in the subsequent high-temperature annealing. The pre-existing δ phase stimulates the nucleation of SRX and hinders the growth of grains. In addition, the second phase particles form a uniform distribution due to dissolution, thereby controlling the difference in grain size. The sufficient pre-precipitation and subsequent uniform dispersion of δ phase achieve a significant grain refinement effect. This paper is expected to serve as a reference for the industrial production of superplastic Inconel 718 sheets.

Recently, the impinging jet has been widely used in the controlled cooling process following hot rolling as a key technology to develop an ultra-fast cooling system. The hot plate/strip undergoes a symmetrically cooling process on the top and bottom surface. Under this consideration, a laboratory apparatus was established to investigate the heat transfer characteristics of a single circular jet impinging on the top or bottom surface of the plate. The results demonstrate that the differences in the heat transfer performance and the wetting front propagation phenomena are noticeable. The top-surface heat flux is slightly higher than the bottom one in the measured cooling region. The heat flux increases with the water flow rate, and decreases with the nozzle-to-surface distance. However, with the increase of radial distance, the top-surface wetting front expanding speed is significantly lower than that of the bottom-surface, especially when the water flow rate is higher than 2 l/min. The results indicate that jet velocity is the critical factor to generate higher cooling performance during both impinging processes. The present study is useful for designing an ultra-fast cooling device and the optimized cooling parameters will enhance the cooling efficiency and cooling uniformity of the industrial ultra-fast cooling equipment.

The heat transfer ability and cooling uniformity in ultra-fast cooling technology played a critical role in improving the microstructure and mechanical properties of hot rolling steel. However, the heat transfer characteristics and boiling phenomena during the cooling process of a water jet impinging on a hot plate surface approximate to the industrial conditions were rarely reported. Herein, we investigated the effect of the initial surface temperature, water temperature, and jet velocity on the heat transfer characteristics for the industrial applications. The results revealed that the rewetting front propagation was considerably affected by the growth and detachment of the bubbles in the rewetting front region. The wetting delay time was extended by the superheat increase, and the sub-cooling and jet velocity decrease, because the ability to condense the bubbles was weakened in the front rewetting region. Meanwhile, the wetting velocity varied with the distance from the stagnant point. Moreover, the maximum heat flux, qmax, was influenced by the initial surface temperature, water temperature, and jet velocity; finally, a regression equation was established to predict the qmax value. The information provided in this work would be beneficial for predicting and optimizing the industrial applications of ultra-fast cooling technology.

A carbon-supported PdSn (PdSn/C) catalyst was prepared by a chemical reduction method with the aid of microwave radiation and was characterized by X-ray diffraction spectroscopy and energy dispersive spectroscopy. Formic acid electrooxidations on PdSn/C and Pd/C catalysts were investigated and compared in an acidic medium by voltammetry and chronoamperometry. The results show that the performance of the PdSn/C-3 catalyst which ratio of Pd:Sn is about 3:1 for formic acid oxidation is greatly improved compared with that of Pd/C; thus, PdSn/C-3 is a promising candidate as an anode catalyst in direct formic acid fuel cells. Additionally, the value of the apparent activation energy shows that the activity of formic acid oxidation on the PdSn/C is sensitive to the temperature at relatively high potentials.

The ultrafast dynamics of the s(1) (n pi*) state of pyridine has been investigated by using ferntosecond time-resolved mass spectrometry and photoelectron imaging combined with (1 + 2') resonance-enhanced multiphoton ionization via the rydberg states. upon excitation into the channel-three region, an ultrafast decay process is observed with a lifetime of about 3.7 ps. the fragment ions show an additional ultrafast decay component. time resolved photoelectron imaging experiments reveal the excited pyridine in channel three region relaxes to an optically dark state on this short time scale. according to previous experimental and theoretical results. we suggest tentatively the ultrafast channel is due to ivr induced fast internal conversion. (c) 2009 elsevier b.v. all rights reserved.

The ultrafast dynamics of chlorobenzene clusters upon 271 nm excitation is studied by femtosecond pump–probe time-of-flight mass spectrometry. Transient profiles of clusters are fitted by two-exponential decay component models, an ultrafast component and a slow decay component. The ultrafast (∼170 fs) decay of S 1 state is tentatively attributed to the internal conversion to the high vibrational levels of S 0 state. Lifetimes of this ultrafast component decease with the cluster size, due to the influence of the solvation effects, while lifetimes of the slow decay component (>1 ns) increase with the cluster size, due to the increase of freedom degrees.

The laser-induced alignment effects of NO in linearly polarized femtosecond laser field within the intensity order of 10 14 W/cm 2 at 820 nm have been investigated experimentally by using velocity mapping technique. The angular and velocity distributions of fragment ions with different charge numbers are measured. The alignment degrees increased with the charge numbers, and were nearly independent of the laser intensities. Our results indicate the geometric alignment dominates before the ionization of NO into NO 2+ , while the dynamic alignment of the molecular ions dominates after the ionization.

The titled reactions are theoretically studied at MP4 (SDTQ) level with 6-311++G(3df,3pd) basis set. All the possible reaction channels are considered for the first time. The most favorable reaction path in H2CO + OH is the channel of producing H2O, which is exothermic by −32.02 kcal/mol, in well agreement with reported experimental result. For H2CO + OH−, the most favorable reaction channel is for H2 molecule formation through several paths. The reaction channels for producing H2 molecule in the titled systems are proposed for the first time. H atom formation in H2CO + OH and hydrogen symmetric transition in H2CO + OH− is also evaluated at higher theory level than literatures.

This paper derives the unbiased estimations of the mean life and the failure rate at a design stress based on the failure censored step-stress accelerated life-testing data. An exponential life distribution with a mean that is a log-linear function of stress, and a cumulative exposure model are assumed. The simulation results show that the maximum likelihood estimations of the mean life and the failure rate at the design stress have positive bias, and the unbiased estimations of the mean life and the failure rate at the design stress have smaller mean squared errors than the maximum likelihood estimations of these parameters in small and moderate samples.