In Mg-Ca alloys the grain refining mechanism,in particular regarding the role of nucleant substrates,remains the object of debates.Although native MgO is being recognised as a nucleating substrate accounting for grain...In Mg-Ca alloys the grain refining mechanism,in particular regarding the role of nucleant substrates,remains the object of debates.Although native MgO is being recognised as a nucleating substrate accounting for grain refinement of Mg alloys,the possible interactions of MgO with alloying elements that may alter the nucleation potency have not been elucidated yet.Herein,we design casting experiments of Mg-xCa alloys varied qualitatively in number density of native MgO,which are then comprehensively studied by advanced electron microscopy.The results show that grain refinement is enhanced as the particle number density of MgO increases.The native MgO particles are modified by interfacial layers due to the co-segregation of Ca and N solute atoms at the MgO/Mg interface.Using aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy,we reveal the nature of these Ca/N interfacial layers at the atomic scale.Irrespective of the crystallographic termination of MgO,Ca and N co-segregate at the MgO/Mg interface and occupy Mg and O sites,respectively,forming an interfacial structure of a few atomic layers.The interfacial structure is slightly expanded,less ordered and defective compared to the MgO matrix due to compositional deviations,whereby the MgO substrate is altered as a poorer template to nucleate Mg solid.Upon solidification in a TP-1 mould,the impotent MgO particles account for the grain refining mechanism,where they are suggested to participate into nucleation and grain initiation processes in an explosive manner.This work not only reveals the atomic engineering of a substrate through interfacial segregation but also demonstrates the effectiveness of a strategy whereby native MgO particles can be harnessed for grain refinement in Mg-Ca alloys.展开更多
为了解安全文化的历史根源及演化情况,以Web of Science中收录的安全文化论文为基础数据,采用参考文献出版年谱分析方法,绘制了1808—2017年的参考文献出版年谱,梳理了整个历史时期对安全文化产生和发展起到重要作用的文献。研究结果表...为了解安全文化的历史根源及演化情况,以Web of Science中收录的安全文化论文为基础数据,采用参考文献出版年谱分析方法,绘制了1808—2017年的参考文献出版年谱,梳理了整个历史时期对安全文化产生和发展起到重要作用的文献。研究结果表明:1808—1979年,安全文化的研究主要引用了早期安全领域的经典著作以及其他领域的方法性成果,是安全文化研究的主要思想来源和方法来源;1980—2017年,出版年谱曲线陡增,出现了大量安全文化研究的经典论文;整体曲线的变化反映了安全文化从概念、模型、方法以及工业实践等方面的研究向医院安全文化实践研究的转变。展开更多
为了解国际安全科学研究的整体产出和分布情况,应用文献计量分析方法,对来自Web of Science的23种安全科学综合期刊2008—2017年的20 432篇论文从年度产出、期刊产出、地理产出分布等维度进行了分析。结果表明,安全科学论文在2008—201...为了解国际安全科学研究的整体产出和分布情况,应用文献计量分析方法,对来自Web of Science的23种安全科学综合期刊2008—2017年的20 432篇论文从年度产出、期刊产出、地理产出分布等维度进行了分析。结果表明,安全科学论文在2008—2017年呈线性增长趋势,AAP、SS、RESS、RA、JLPPI是安全科学论文的主要载体。在空间分布上,美国、中国、英格兰、澳大利亚及加拿大等是安全论文的主要产出国家/地区,且美国和中国在时间趋势上的表现要优于其他国家/地区。美国德克萨斯A＆M大学、荷兰代尔夫特理工大学、挪威斯塔万格大学、意大利米兰理工大学及澳大利亚莫纳什大学等机构论文产出表现突出。但在时间趋势上,机构的产出表现出了显著的波动。我国机构中国科学院和清华大学位于高产行列,但研究产出的出处并非我国传统的安全科学与工程专业所在机构。在今后的研究中,我国需要进一步融入国际安全科学研究主流,提升国际安全科学影响力。展开更多
基金financial support under grant number EP/N007638/1supported by EPSRC under grant number EP/W021080/1
文摘In Mg-Ca alloys the grain refining mechanism,in particular regarding the role of nucleant substrates,remains the object of debates.Although native MgO is being recognised as a nucleating substrate accounting for grain refinement of Mg alloys,the possible interactions of MgO with alloying elements that may alter the nucleation potency have not been elucidated yet.Herein,we design casting experiments of Mg-xCa alloys varied qualitatively in number density of native MgO,which are then comprehensively studied by advanced electron microscopy.The results show that grain refinement is enhanced as the particle number density of MgO increases.The native MgO particles are modified by interfacial layers due to the co-segregation of Ca and N solute atoms at the MgO/Mg interface.Using aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy,we reveal the nature of these Ca/N interfacial layers at the atomic scale.Irrespective of the crystallographic termination of MgO,Ca and N co-segregate at the MgO/Mg interface and occupy Mg and O sites,respectively,forming an interfacial structure of a few atomic layers.The interfacial structure is slightly expanded,less ordered and defective compared to the MgO matrix due to compositional deviations,whereby the MgO substrate is altered as a poorer template to nucleate Mg solid.Upon solidification in a TP-1 mould,the impotent MgO particles account for the grain refining mechanism,where they are suggested to participate into nucleation and grain initiation processes in an explosive manner.This work not only reveals the atomic engineering of a substrate through interfacial segregation but also demonstrates the effectiveness of a strategy whereby native MgO particles can be harnessed for grain refinement in Mg-Ca alloys.
文摘为了解安全文化的历史根源及演化情况,以Web of Science中收录的安全文化论文为基础数据,采用参考文献出版年谱分析方法,绘制了1808—2017年的参考文献出版年谱,梳理了整个历史时期对安全文化产生和发展起到重要作用的文献。研究结果表明:1808—1979年,安全文化的研究主要引用了早期安全领域的经典著作以及其他领域的方法性成果,是安全文化研究的主要思想来源和方法来源;1980—2017年,出版年谱曲线陡增,出现了大量安全文化研究的经典论文;整体曲线的变化反映了安全文化从概念、模型、方法以及工业实践等方面的研究向医院安全文化实践研究的转变。
文摘为了解国际安全科学研究的整体产出和分布情况,应用文献计量分析方法,对来自Web of Science的23种安全科学综合期刊2008—2017年的20 432篇论文从年度产出、期刊产出、地理产出分布等维度进行了分析。结果表明,安全科学论文在2008—2017年呈线性增长趋势,AAP、SS、RESS、RA、JLPPI是安全科学论文的主要载体。在空间分布上,美国、中国、英格兰、澳大利亚及加拿大等是安全论文的主要产出国家/地区,且美国和中国在时间趋势上的表现要优于其他国家/地区。美国德克萨斯A＆M大学、荷兰代尔夫特理工大学、挪威斯塔万格大学、意大利米兰理工大学及澳大利亚莫纳什大学等机构论文产出表现突出。但在时间趋势上,机构的产出表现出了显著的波动。我国机构中国科学院和清华大学位于高产行列,但研究产出的出处并非我国传统的安全科学与工程专业所在机构。在今后的研究中,我国需要进一步融入国际安全科学研究主流,提升国际安全科学影响力。
