Dedicated to Dr Gerhard Herzberg on the occasion of his 90th birthday Recent large-scale ab initio calculations for small negative molecular ions are reviewed. Accurate equilibrium geometries are established for several species like NH; , HCC -, NO;, CH2N -, C; and C , . Predictions are made for various spectroscopic properties like vibrational frequencies, rotational constants and infrared intensities. The effects of a shallow energy minimum in the T-shaped configuration on the rovibrational term energies of HCC -are investigated. The calculated vibrational structures of the photoelectron spectra of SiH; and CH2N -are in very good agreement with the experiment. The present calculations support t$e assig_nment of an absorption observed at 608nm in a neon matrix to the C2n, t X'I'I, transition of C, . Electron affinities are obtained with an accuracy of 0.05eV or better. Spectroscopic properties of intermediates in simple S,2 reactions are calculated.
Abstract:The effect of heating rate on the formation and decomposition of austenite was investigated on cold-rolled low carbon steel. Experiments were performed at two heating rates, 150 • C/s and 1500 • C/s, respectively. The microstructures were characterized by means of scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Experimental evidence of nucleation of austenite in α/θ, as well as in α/α boundaries is analyzed from the thermodynamic point of view. The increase in the heating rates from 150 • C/s to 1500 • C/s has an impact on the morphology of austenite in the intercritical range. The effect of heating rate on the austenite formation mechanism is analyzed combining thermodynamic calculations and experimental data. The results provide indirect evidence of a transition in the mechanism of austenite formation, from carbon diffusion control to interface control mode. The resulting microstructure after the application of ultrafast heating rates is complex and consists of a mixture of ferrite with different morphologies, undissolved cementite, martensite, and retained austenite.
This paper presents an experimental and numerical study of the solidification process of ductile cast iron under slightly hypereutectic conditions. The material thermo-microstructural behaviour is measured in tests performed using standardized cups. Cooling curves at the centre of the cup were recorded, and metallographic studies were carried out to investigate the number and size of graphite nodules at the end of the process. Different models were tested: a model based on a uninodular theory and two models which represent the multi-nodular theory. The cooling curves predicted by these models are in good agreement with the experimental measurements. Some scatter is found, however, in the numerical-experimental comparison for the graphite nodule density at different points of the sample.
OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This work presents an experimental and numerical study of the solidification process of an eutectic spheroidal graphite cast iron (SGI). The effect of the cooling rate on the thermal-microstructural response is particularly analysed. To this end, experiments as well as numerical simulations were carried out. The experiments consisted in a solidification test in a wedge-like casting such that different cooling rates were measured at specific positions along the part. A metallographic analysis was also performed in five locations of the sample with the aim of obtaining the number and size of graphite nodules at the end of the process. The numerical simulations were made using multinodular based and uninodular based models. These two models predicted similar results in terms of cooling curves and nodule counts. Besides, good experimental-numerical agreements were obtained for both the cooling curves and the graphite nodule counts.
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