The quantity and morphology of spheroidal graphite have an important effect on the properties of ductile iron, and the characteristics of spheroidal graphite are determined by the solidification process. The aim of th...The quantity and morphology of spheroidal graphite have an important effect on the properties of ductile iron, and the characteristics of spheroidal graphite are determined by the solidification process. The aim of this work is to explore the precipitation and evolution of graphite nodules in hypoeutectic, eutectic, and hypereutectic ductile irons by thermal analysis, liquid quenching and metallographic technique. Results show that hypoeutectic ductile iron has the longest solidification time and the lowest eutectic temperature;eutectic ductile iron has the shortest solidification time;hypereutectic ductile iron has the highest eutectic temperature. After solidification is completed, hypoeutectic ductile iron has the lowest nodule count, nodularity and graphite fraction;eutectic ductile iron has the highest nodule count, nodularity and the smallest nodule diameter;hypereutectic has the highest nodule diameter and graphite fraction. The nucleation and growth of graphite nodules in hypereutectic ductile iron starts before bulk eutectic crystallization stage, however, the precipitation and evolution of graphite nodules of hypoeutectic and eutectic ductile irons mainly occur in the eutectic crystallization stage. The graphite precipitated in eutectic crystallization of hypoeutectic, eutectic, and hypereutectic ductile irons, are 61%, 68% and 43% of total graphite volume fraction, respectively. Simultaneously, there are plenty of austenite dendrites in hypoeutectic and hypereutectic ductile irons, which are prone to shrinkage defects. Therefore, the eutectic ductile iron has the smallest shrinkage tendency.展开更多
A gold tube simulation device was used to study the cleavage of representative compounds into gas.The goal of this study is to investigate hydrogen isotope composition change of gaseous hydrocarbons during maturity.Ga...A gold tube simulation device was used to study the cleavage of representative compounds into gas.The goal of this study is to investigate hydrogen isotope composition change of gaseous hydrocarbons during maturity.Gas chromatography and isotopic analyses were conducted to determine how the yield of natural gas components and their hydrogen isotopic composition were related to experimental temperature and heating rate.A chemical kinetic model for the generation of each component of the natural gas and for the hydrogen isotopic fractionation was established and calibrated based on the results.Results indicate that the hydrogen isotopic fractionation during the evolution of various gas-forming organic materials can be satisfactorily described by chemical kinetic models.During regular methane generation,the reactions at low-activation-energy region had a greater contribution than the high-activation-energy region.While the reactions with high-activation-energy region had greater contribution of deuterium-rich methane.Compared with carbon isotope fractionation,this results in a greater hydrogen isotopic fractionation,which is more sensitive to changes in maturity.This study lays a foundation for further investigations of genesis and maturity of natural gas provided by hydrogen isotopic fractionation.It also provides fundamental knowledge for investigating the filling history of natural gas reservoir and for identifying.展开更多
This study focused on the synergistic effect of alloying elements neodymium(Nd) and dysprosium(Dy) on the ignition-proof performance of AZ91D alloy. The ignition-proof mechanism of AZ91D-3 Nd-x Dy(x = 0.5, 1.0, 1.5, 2...This study focused on the synergistic effect of alloying elements neodymium(Nd) and dysprosium(Dy) on the ignition-proof performance of AZ91D alloy. The ignition-proof mechanism of AZ91D-3 Nd-x Dy(x = 0.5, 1.0, 1.5, 2.0 and 2.5 wt.%) alloy was discussed in depth through ignition-proof testing and microstructure observation. The results showed that the AZ91D-3 Nd-2 Dy alloy exhibited the highest ignition-point of 893 K, increased by 69 K as compared to the AZ91D alloy. The ignition-proof mechanism of Nd and Dy additions lay in three aspects:(1) the formation of denser oxide film consisting of Dy_2O_3 and MgO improves the oxidation resistance of the alloy,(2) the great reduction of the low melting-point phase β-Mg_(17)Al_(12), which leads to the decrease in the oxygen diffusion channels, and(3) the newly formed high melting-point phases(Al_2Nd and Al_2Dy), which block the oxygen diffusion channels and prevent the chemical reaction of Mg and oxygen.展开更多
基金This work was financially supported by the National Natural Science F oundation of China(NSFC)under Grant Nos.51601054 and 51775006the Natural Science Foundation of Hebei Province of China under Grant Nos.E2017202095 and E2016202100+1 种基金the Scientific and Technological Transformative Project of Tianjin Supporting Bijing-Tianjin-Hebei under Grant No.18YFCZZC00030the Central Government Guides I.ocal Science and Technology Development Fund Projects under Grant No.206Z 1005G.
文摘The quantity and morphology of spheroidal graphite have an important effect on the properties of ductile iron, and the characteristics of spheroidal graphite are determined by the solidification process. The aim of this work is to explore the precipitation and evolution of graphite nodules in hypoeutectic, eutectic, and hypereutectic ductile irons by thermal analysis, liquid quenching and metallographic technique. Results show that hypoeutectic ductile iron has the longest solidification time and the lowest eutectic temperature;eutectic ductile iron has the shortest solidification time;hypereutectic ductile iron has the highest eutectic temperature. After solidification is completed, hypoeutectic ductile iron has the lowest nodule count, nodularity and graphite fraction;eutectic ductile iron has the highest nodule count, nodularity and the smallest nodule diameter;hypereutectic has the highest nodule diameter and graphite fraction. The nucleation and growth of graphite nodules in hypereutectic ductile iron starts before bulk eutectic crystallization stage, however, the precipitation and evolution of graphite nodules of hypoeutectic and eutectic ductile irons mainly occur in the eutectic crystallization stage. The graphite precipitated in eutectic crystallization of hypoeutectic, eutectic, and hypereutectic ductile irons, are 61%, 68% and 43% of total graphite volume fraction, respectively. Simultaneously, there are plenty of austenite dendrites in hypoeutectic and hypereutectic ductile irons, which are prone to shrinkage defects. Therefore, the eutectic ductile iron has the smallest shrinkage tendency.
基金the National Natural Science Foundation of China(41672130,41772131)the National Oil and Gas Major Project(2016ZX05061-003-001,2016ZX05029002-002)+1 种基金the Sinopec Scientific and Technological Research Project(P17027-3)the Ministry of Education’s Independent Innovation Fund Project(14CX02224A)for financial support of this study。
文摘A gold tube simulation device was used to study the cleavage of representative compounds into gas.The goal of this study is to investigate hydrogen isotope composition change of gaseous hydrocarbons during maturity.Gas chromatography and isotopic analyses were conducted to determine how the yield of natural gas components and their hydrogen isotopic composition were related to experimental temperature and heating rate.A chemical kinetic model for the generation of each component of the natural gas and for the hydrogen isotopic fractionation was established and calibrated based on the results.Results indicate that the hydrogen isotopic fractionation during the evolution of various gas-forming organic materials can be satisfactorily described by chemical kinetic models.During regular methane generation,the reactions at low-activation-energy region had a greater contribution than the high-activation-energy region.While the reactions with high-activation-energy region had greater contribution of deuterium-rich methane.Compared with carbon isotope fractionation,this results in a greater hydrogen isotopic fractionation,which is more sensitive to changes in maturity.This study lays a foundation for further investigations of genesis and maturity of natural gas provided by hydrogen isotopic fractionation.It also provides fundamental knowledge for investigating the filling history of natural gas reservoir and for identifying.
文摘This study focused on the synergistic effect of alloying elements neodymium(Nd) and dysprosium(Dy) on the ignition-proof performance of AZ91D alloy. The ignition-proof mechanism of AZ91D-3 Nd-x Dy(x = 0.5, 1.0, 1.5, 2.0 and 2.5 wt.%) alloy was discussed in depth through ignition-proof testing and microstructure observation. The results showed that the AZ91D-3 Nd-2 Dy alloy exhibited the highest ignition-point of 893 K, increased by 69 K as compared to the AZ91D alloy. The ignition-proof mechanism of Nd and Dy additions lay in three aspects:(1) the formation of denser oxide film consisting of Dy_2O_3 and MgO improves the oxidation resistance of the alloy,(2) the great reduction of the low melting-point phase β-Mg_(17)Al_(12), which leads to the decrease in the oxygen diffusion channels, and(3) the newly formed high melting-point phases(Al_2Nd and Al_2Dy), which block the oxygen diffusion channels and prevent the chemical reaction of Mg and oxygen.