In this study, austenitizing heat treatment before hot stamping of Al-10% Si coated boron steel is first investigated through en- vironment scanning electron microscopy （ESEM） equipped with energy dispersive x-ray a...In this study, austenitizing heat treatment before hot stamping of Al-10% Si coated boron steel is first investigated through en- vironment scanning electron microscopy （ESEM） equipped with energy dispersive x-ray analysis （EDAX）. The cracking be- havior of the coating was evaluated using Gleeble 3500, a thermo-mechanical simulator under uniaxial plastic deformation at elevated temperatures. The extent and number of cracks developed in the coating were carefully assessed through an optical microscope. The coating layer under hot-dipped condition consists of an Al-Si eutectic matrix, Fe2Al7Si, Fe3Al2Si3 and Fe2Al5, from the coating surface to the steel substrate. The coating layer remains dense, continuous and smooth. During austenitization, the Al-rich Fe-Al intermetallics in the coating transform to more Fe-rich intermetallics, promoted by the Fe diffusion process. The coating finally shows the coexistence of two types of Fe-Al intermetallics, namely, FeAl2 and FeAl. Microcracks and Kirkendall voids occur in the coating layer and diffusion zone, respectively. The coating is heavily cracked and broken into segments during the hot tensile tests. Bare steel exposed between the separate segments of the coating is oxidized and covered with a thin FeOx layer. The appearance of the oxide decreases the adhesion of the Al-Si coating. It is found that the ductile FeAl is preferred as a coating microstructure instead of the brittle FeAl2. Therefore, the ductility of the Al-Si coating on hot stamping boron steer could be enhanced by controlling the ductile Fe-rich intermetallic phase transformations within it during austenitization. Experiments indicate that a higher austenitizing temperature or longer dwell time facilitate the Fe-rich inter- metallics transformation, increasing the volume fraction of FeAl. This phase transformation also contributes to reducing the crack density and depth.展开更多
Aluminum-rich chondrules （ARCs）, which share mineralogic and chemical properties with both Ca, Al-rich inclusions （CAIs） and ferromagnesian chondrules, play an important role in revealing their temporal and petrog...Aluminum-rich chondrules （ARCs）, which share mineralogic and chemical properties with both Ca, Al-rich inclusions （CAIs） and ferromagnesian chondrules, play an important role in revealing their temporal and petrogenetic relationships. In this work, seven ARCs were found in three ordinary chondrites GRV 022410 （H4）, GRV 052722 （H3.7） and Julesburg （L3.6）. They contain bulk Al2O3 - 17%-33% and exhibit igneous textures composed of olivine, high- and low-Ca pyroxene, plagioclase, spinel and glass. In situ SIMS analyses show that ARCs have oxygen isotopic compositions （δ18O=-6.1‰-7.1‰; δ17O= -4.5‰-5.1‰） close to ferromagnesian chondrules but far more depleted in 160 than CAIs （δ18O=-40‰; δ17O=-40‰）. Most ARCs plot close to the terrestrial mass fractionation （TF） line, and a few between the TF and carbonaceous chondrite anhydrous mixing （CCAM） lines. Plagioclase, nepheline and glass suffered O-isotopic exchanges during the metamorphism processes in the parent body. Spinel, olivine and pyroxene represent the primary O-isotopic compositions of ARCs, and define a fitted line with a slope of- 0.7±0.1. Compared with the results of previous studies, shallower slope as well as more depleted 160 compositions further demonstrates that ARCs in ordinary chondrites are not a simple mixing product of ferromagnesian chondrules and CAIs. Instead, they probably experienced higher-degree oxygen isotope exchange with a δ6O-poor nebular gas reservoir during multiple melting episodes.展开更多
High concentrations of antimony(Sb) in soils and vegetables can cause potential health risk. However, the effect of Sb on the growth and response of crops are not well known and to date, there is still no Sb limit sta...High concentrations of antimony(Sb) in soils and vegetables can cause potential health risk. However, the effect of Sb on the growth and response of crops are not well known and to date, there is still no Sb limit standard for Allitic Udic Ferrisols in China. In this study, a greenhouse experiment was carried out to investigate the effect of antimony(Sb) on biomass, physiological performances,and macro- and micronutrient element concentrations of green Chinese cabbage(Brassica chinensis L.), as well as enzyme activities,in Allitic Udic Ferrisols from Hunan Province, China. Antimony was supplied at rates of 0(control), 2, 5, 10, 20, and 50 mg kg-1and thus with the background value of 1.0 mg kg-1, the Sb concentrations in the treated soil samples were 1, 3, 6, 11 21, and 51 mg kg-1, respectively. The results showed the leaf biomass and ascorbic acid content of cabbage significantly(P < 0.05) decreased by 30.6% and 48.3%, respectively, and soil urease and dehydrogenase activities also significantly(P < 0.05) decreased by 33.6%and 32.5%, respectively, when soil Sb concentration was 21 mg kg-1as compared with the control. The uptake of essential nutrient elements such as Mg, Cu, and Zn by cabbage was obviously affected, while the leaf soluble sugar content slightly changed when the soil Sb concentration exceeded 21 mg kg-1. Based on cabbage physiological responses and soil enzyme activities, the permissible concentration of 21 mg kg-1for Sb in Allitic Udic Ferrisols should be recommended.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51275185)the National Basic Research Program of China("973"Program)(Grant No.2010CB630802-3)
文摘In this study, austenitizing heat treatment before hot stamping of Al-10% Si coated boron steel is first investigated through en- vironment scanning electron microscopy （ESEM） equipped with energy dispersive x-ray analysis （EDAX）. The cracking be- havior of the coating was evaluated using Gleeble 3500, a thermo-mechanical simulator under uniaxial plastic deformation at elevated temperatures. The extent and number of cracks developed in the coating were carefully assessed through an optical microscope. The coating layer under hot-dipped condition consists of an Al-Si eutectic matrix, Fe2Al7Si, Fe3Al2Si3 and Fe2Al5, from the coating surface to the steel substrate. The coating layer remains dense, continuous and smooth. During austenitization, the Al-rich Fe-Al intermetallics in the coating transform to more Fe-rich intermetallics, promoted by the Fe diffusion process. The coating finally shows the coexistence of two types of Fe-Al intermetallics, namely, FeAl2 and FeAl. Microcracks and Kirkendall voids occur in the coating layer and diffusion zone, respectively. The coating is heavily cracked and broken into segments during the hot tensile tests. Bare steel exposed between the separate segments of the coating is oxidized and covered with a thin FeOx layer. The appearance of the oxide decreases the adhesion of the Al-Si coating. It is found that the ductile FeAl is preferred as a coating microstructure instead of the brittle FeAl2. Therefore, the ductility of the Al-Si coating on hot stamping boron steer could be enhanced by controlling the ductile Fe-rich intermetallic phase transformations within it during austenitization. Experiments indicate that a higher austenitizing temperature or longer dwell time facilitate the Fe-rich inter- metallics transformation, increasing the volume fraction of FeAl. This phase transformation also contributes to reducing the crack density and depth.
基金supported by the Natural Science Foundation of Jiangsu Province(Grant No.BK20131040)the National Natural Science Foundation of China(Grants Nos.41403056,41173076,41273079,41003026)the Minor Planet Foundation of China
文摘Aluminum-rich chondrules （ARCs）, which share mineralogic and chemical properties with both Ca, Al-rich inclusions （CAIs） and ferromagnesian chondrules, play an important role in revealing their temporal and petrogenetic relationships. In this work, seven ARCs were found in three ordinary chondrites GRV 022410 （H4）, GRV 052722 （H3.7） and Julesburg （L3.6）. They contain bulk Al2O3 - 17%-33% and exhibit igneous textures composed of olivine, high- and low-Ca pyroxene, plagioclase, spinel and glass. In situ SIMS analyses show that ARCs have oxygen isotopic compositions （δ18O=-6.1‰-7.1‰; δ17O= -4.5‰-5.1‰） close to ferromagnesian chondrules but far more depleted in 160 than CAIs （δ18O=-40‰; δ17O=-40‰）. Most ARCs plot close to the terrestrial mass fractionation （TF） line, and a few between the TF and carbonaceous chondrite anhydrous mixing （CCAM） lines. Plagioclase, nepheline and glass suffered O-isotopic exchanges during the metamorphism processes in the parent body. Spinel, olivine and pyroxene represent the primary O-isotopic compositions of ARCs, and define a fitted line with a slope of- 0.7±0.1. Compared with the results of previous studies, shallower slope as well as more depleted 160 compositions further demonstrates that ARCs in ordinary chondrites are not a simple mixing product of ferromagnesian chondrules and CAIs. Instead, they probably experienced higher-degree oxygen isotope exchange with a δ6O-poor nebular gas reservoir during multiple melting episodes.
基金supported by the National Natural Science Foundation of China(No.41201492)the Science and Technology Project of Changsha City,China(No.K1003056-31)
文摘High concentrations of antimony(Sb) in soils and vegetables can cause potential health risk. However, the effect of Sb on the growth and response of crops are not well known and to date, there is still no Sb limit standard for Allitic Udic Ferrisols in China. In this study, a greenhouse experiment was carried out to investigate the effect of antimony(Sb) on biomass, physiological performances,and macro- and micronutrient element concentrations of green Chinese cabbage(Brassica chinensis L.), as well as enzyme activities,in Allitic Udic Ferrisols from Hunan Province, China. Antimony was supplied at rates of 0(control), 2, 5, 10, 20, and 50 mg kg-1and thus with the background value of 1.0 mg kg-1, the Sb concentrations in the treated soil samples were 1, 3, 6, 11 21, and 51 mg kg-1, respectively. The results showed the leaf biomass and ascorbic acid content of cabbage significantly(P < 0.05) decreased by 30.6% and 48.3%, respectively, and soil urease and dehydrogenase activities also significantly(P < 0.05) decreased by 33.6%and 32.5%, respectively, when soil Sb concentration was 21 mg kg-1as compared with the control. The uptake of essential nutrient elements such as Mg, Cu, and Zn by cabbage was obviously affected, while the leaf soluble sugar content slightly changed when the soil Sb concentration exceeded 21 mg kg-1. Based on cabbage physiological responses and soil enzyme activities, the permissible concentration of 21 mg kg-1for Sb in Allitic Udic Ferrisols should be recommended.
