The effect of Al on the morphology of MnS in medium-carbon non-quenched and tempered steel was investigated at three different cooling rates of 0.24, 0.43, and 200°C·s^-1. The formation mechanisms of three t...The effect of Al on the morphology of MnS in medium-carbon non-quenched and tempered steel was investigated at three different cooling rates of 0.24, 0.43, and 200°C·s^-1. The formation mechanisms of three types of MnS were elucidated based on phase diagram information combined with crystal growth models. The morphology of MnS is governed by the precipitation mode and the growth conditions. A monotectic reaction and subsequent fast solidification lead to globular Type I MnS. Type II MnS inclusions with different morphological characteristics form as a result of a eutectic reaction followed by the growth in the Fe matrix. Type III MnS presents a divorced eutectic morphology. At the cooling rate of 0.24°C·s^-1, the precipitation of dispersed Type III MnS is significantly enhanced by the addition of 0.044wt% acid-soluble Al（Als）, while Type II MnS clusters prefer to form in steels with either 0.034wt% or 0.052wt% Als. At the relatively higher cooling rates of 200°C·s^-1 and 0.43°C·s^-1, the formation of Type I and Type II MnS inclusions is promoted, and the influence of Al is negligible. The results of this work are expected to be employed in practice to improve the mechanical properties of non-quenched and tempered steels.展开更多
Studying the first generation of stars, galaxies and supermassive black holes as well as the epoch of reionization is one of the fundamental questions of modern as- trophysics. The last few years have witnessed the fi...Studying the first generation of stars, galaxies and supermassive black holes as well as the epoch of reionization is one of the fundamental questions of modern as- trophysics. The last few years have witnessed the first confirmation of the discoveries of galaxies, quasars and Gamma-Ray Bursts at z 〉 7, with possible detections at z - 10. There is also mounting evidence that cosmic reionization is a prolonged pro- cess that peaks around z - 10 and ends at z- 6 - 7. Observations of the highest redshift intergalactic medium and the most metal-poor stars in the Galaxy begin to constrain the earliest chemical enrichment processes in the Universe. These observa- tions provide a glimpse of cosmic history over the first billion years after the Big Bang. In this review, we will present recent results on the observations of the high-redshift Universe over the past decade, highlight key challenges and uncertainties in these observations, and preview what is possible with the next generation facilities in studying the first light and mapping the history of reionization.展开更多
基金financially supported by the National Natural Science Foundation of China (Nos. 51174020 and 51374018)the National High-Tech Research and Development Program of China (No. 2013AA031601)
文摘The effect of Al on the morphology of MnS in medium-carbon non-quenched and tempered steel was investigated at three different cooling rates of 0.24, 0.43, and 200°C·s^-1. The formation mechanisms of three types of MnS were elucidated based on phase diagram information combined with crystal growth models. The morphology of MnS is governed by the precipitation mode and the growth conditions. A monotectic reaction and subsequent fast solidification lead to globular Type I MnS. Type II MnS inclusions with different morphological characteristics form as a result of a eutectic reaction followed by the growth in the Fe matrix. Type III MnS presents a divorced eutectic morphology. At the cooling rate of 0.24°C·s^-1, the precipitation of dispersed Type III MnS is significantly enhanced by the addition of 0.044wt% acid-soluble Al（Als）, while Type II MnS clusters prefer to form in steels with either 0.034wt% or 0.052wt% Als. At the relatively higher cooling rates of 200°C·s^-1 and 0.43°C·s^-1, the formation of Type I and Type II MnS inclusions is promoted, and the influence of Al is negligible. The results of this work are expected to be employed in practice to improve the mechanical properties of non-quenched and tempered steels.
基金supported by a David and Lucile Packard Fellowshipthe US National Science Foundation (NSF) Grants AST 08-06861 and AST 11-07682
文摘Studying the first generation of stars, galaxies and supermassive black holes as well as the epoch of reionization is one of the fundamental questions of modern as- trophysics. The last few years have witnessed the first confirmation of the discoveries of galaxies, quasars and Gamma-Ray Bursts at z 〉 7, with possible detections at z - 10. There is also mounting evidence that cosmic reionization is a prolonged pro- cess that peaks around z - 10 and ends at z- 6 - 7. Observations of the highest redshift intergalactic medium and the most metal-poor stars in the Galaxy begin to constrain the earliest chemical enrichment processes in the Universe. These observa- tions provide a glimpse of cosmic history over the first billion years after the Big Bang. In this review, we will present recent results on the observations of the high-redshift Universe over the past decade, highlight key challenges and uncertainties in these observations, and preview what is possible with the next generation facilities in studying the first light and mapping the history of reionization.
