To obtain the billet with homogeneous and spheroidized primary grains is the key step in the semi-solid forming process. Among the semi-solid billet preparation methods, the process of low-superheat direct chill (DC) ...To obtain the billet with homogeneous and spheroidized primary grains is the key step in the semi-solid forming process. Among the semi-solid billet preparation methods, the process of low-superheat direct chill (DC) casting is simpler and more effective. In this study, the billets of AlSi7Mg alloy were prepared by low-superheat DC casting at various withdrawal rates. The effect of withdrawal rate on the surface quality of the billets was investigated, and the evolution mechanism of the microstructural morphology in the billets was analyzed. The results show that the periodic corrugations and a large quantity of fine shrinkage pits appear in the billet surface when the withdrawal rate is 100 mm·min-1, and the above defects in the billet surface can be eliminated completely when the withdrawal rate is above 150 mm·min-1. But when the withdrawal rate is too fast (250 mm·min-1), the primary α grains, except the ones in the billet center, have not enough time for ripening due to the high silidification rate, and will solidify as the dendrite structure. When the withdrawal rate is between 150 - 200 mm·min-1, the dendritic growth of the primary α grains is effectively inhibited, and a billet of AlSi7Mg alloy with a smooth surface and homogeneous, fine, non-dendritic grains can be obtained.展开更多
Al-4.5wt.%Cu alloy has been directionally solidified at constant and abruptly changing withdrawal rates, respectively. The effects of the withdrawal rate on solidification microstructure, primary dendrite arm spacing(...Al-4.5wt.%Cu alloy has been directionally solidified at constant and abruptly changing withdrawal rates, respectively. The effects of the withdrawal rate on solidification microstructure, primary dendrite arm spacing(PDAS) and liquid solute distribution in front of the solid-liquid interface were investigated. The experimental results for the PDAS at a constant withdrawal rate agree well with the values calculated by the Hunt, Trivedi and Hunt-Lu models. At an abrupt change in the withdrawal rate, the maximum to minimum ratio of the PDAS at a given solidification parameter, i.e. λ1max/λ1min, is more than 2, and the PDAS values are remarkably history-dependent. Further, the liquid-solute distribution curve based on theoretical calculation shows that the larger the initial withdrawal rate is, the smaller the minimum of liquid solute concentration in front of the solid-liquid interface is after the abrupt change in withdrawal rate.展开更多
In order to study the effect of the withdrawing rate on carbide morphology,MC-type carbide in single crystal superalloy AM3 was systematically investigated with sample growth rates from 3.5 μm/s to 500 μm/s.The carb...In order to study the effect of the withdrawing rate on carbide morphology,MC-type carbide in single crystal superalloy AM3 was systematically investigated with sample growth rates from 3.5 μm/s to 500 μm/s.The carbide morphologies were investigated by scanning electron microscopy(SEM),and the electron probe microanalysis(EPMA) was used to characterize the carbide composition.The results indicate that the solidification rate is the important factor governing MC carbide growth morphology,size and distribution,composition and growth mechanism.With the increase of withdrawing rate,nodular,rod-like,Chinese script types of carbide morphology are observed.For the low withdrawing rate,with the increase of withdrawing rate,the carbide size becomes larger.For the case of dendritic interface,the carbide size becomes smaller with refinement of dendrites as withdrawing rate increases.The volume fraction of carbides increases with the withdrawing rate increasing.展开更多
目的:降低我院住院药房退药率,提升医药护团队服务效率。方法:通过住院药房医院信息系统(hospital information system,HIS)比较实施PDCA退药管理措施前后1年的退药原因和频次,以及年(月)退药率。结果:改治疗方案、药房无药和患者出院...目的:降低我院住院药房退药率,提升医药护团队服务效率。方法:通过住院药房医院信息系统(hospital information system,HIS)比较实施PDCA退药管理措施前后1年的退药原因和频次,以及年(月)退药率。结果:改治疗方案、药房无药和患者出院为退药主要原因;实施PDCA退药管理后,住院药房年退药率低于实施前,且随着PDCA循环增加,月退药率持续降低(P<0.05)。结论:采取退药管理PDCA方法可有效降低住院药房退药率,促进医务团队服务水平提升。展开更多
利用高温度梯度定向凝固技术——液态金属冷却LMC(liquid metal cooling)技术制备了单晶铸件,采用ProCAST有限元模拟软件包计算了LMC定向凝固工艺下,不同抽拉速度单晶高温合金铸件定向凝固过程的温度场,预测了拉速对单晶生长缺陷的影响...利用高温度梯度定向凝固技术——液态金属冷却LMC(liquid metal cooling)技术制备了单晶铸件,采用ProCAST有限元模拟软件包计算了LMC定向凝固工艺下,不同抽拉速度单晶高温合金铸件定向凝固过程的温度场,预测了拉速对单晶生长缺陷的影响。结果表明,模拟结果与实验结果吻合良好,计算的温度曲线在1100℃以上与实测温度曲线相比误差小于5%;随着抽拉速度的增加,凝固界面下凹,曲率增加,铸件缘板处出现杂晶的倾向增大。展开更多
基金supported by the Postdoctoral Foundation of Northeastern University and the National High Technology Research and Development Program of China(Grant No.2009BAE80B01)
文摘To obtain the billet with homogeneous and spheroidized primary grains is the key step in the semi-solid forming process. Among the semi-solid billet preparation methods, the process of low-superheat direct chill (DC) casting is simpler and more effective. In this study, the billets of AlSi7Mg alloy were prepared by low-superheat DC casting at various withdrawal rates. The effect of withdrawal rate on the surface quality of the billets was investigated, and the evolution mechanism of the microstructural morphology in the billets was analyzed. The results show that the periodic corrugations and a large quantity of fine shrinkage pits appear in the billet surface when the withdrawal rate is 100 mm·min-1, and the above defects in the billet surface can be eliminated completely when the withdrawal rate is above 150 mm·min-1. But when the withdrawal rate is too fast (250 mm·min-1), the primary α grains, except the ones in the billet center, have not enough time for ripening due to the high silidification rate, and will solidify as the dendrite structure. When the withdrawal rate is between 150 - 200 mm·min-1, the dendritic growth of the primary α grains is effectively inhibited, and a billet of AlSi7Mg alloy with a smooth surface and homogeneous, fine, non-dendritic grains can be obtained.
基金financially supported by the National Natural Science Foundation of China(No.50971101)the Specialized Research Fund for the Doctoral Program of Higher Education(No.20136102110014)
文摘Al-4.5wt.%Cu alloy has been directionally solidified at constant and abruptly changing withdrawal rates, respectively. The effects of the withdrawal rate on solidification microstructure, primary dendrite arm spacing(PDAS) and liquid solute distribution in front of the solid-liquid interface were investigated. The experimental results for the PDAS at a constant withdrawal rate agree well with the values calculated by the Hunt, Trivedi and Hunt-Lu models. At an abrupt change in the withdrawal rate, the maximum to minimum ratio of the PDAS at a given solidification parameter, i.e. λ1max/λ1min, is more than 2, and the PDAS values are remarkably history-dependent. Further, the liquid-solute distribution curve based on theoretical calculation shows that the larger the initial withdrawal rate is, the smaller the minimum of liquid solute concentration in front of the solid-liquid interface is after the abrupt change in withdrawal rate.
基金Projects(50771081, 50931004) supported by the National Natural Science Foundation of ChinaProject(2010CB631202) supported by the National Basic Research Program of China
文摘In order to study the effect of the withdrawing rate on carbide morphology,MC-type carbide in single crystal superalloy AM3 was systematically investigated with sample growth rates from 3.5 μm/s to 500 μm/s.The carbide morphologies were investigated by scanning electron microscopy(SEM),and the electron probe microanalysis(EPMA) was used to characterize the carbide composition.The results indicate that the solidification rate is the important factor governing MC carbide growth morphology,size and distribution,composition and growth mechanism.With the increase of withdrawing rate,nodular,rod-like,Chinese script types of carbide morphology are observed.For the low withdrawing rate,with the increase of withdrawing rate,the carbide size becomes larger.For the case of dendritic interface,the carbide size becomes smaller with refinement of dendrites as withdrawing rate increases.The volume fraction of carbides increases with the withdrawing rate increasing.
文摘目的:降低我院住院药房退药率,提升医药护团队服务效率。方法:通过住院药房医院信息系统(hospital information system,HIS)比较实施PDCA退药管理措施前后1年的退药原因和频次,以及年(月)退药率。结果:改治疗方案、药房无药和患者出院为退药主要原因;实施PDCA退药管理后,住院药房年退药率低于实施前,且随着PDCA循环增加,月退药率持续降低(P<0.05)。结论:采取退药管理PDCA方法可有效降低住院药房退药率,促进医务团队服务水平提升。
文摘利用高温度梯度定向凝固技术——液态金属冷却LMC(liquid metal cooling)技术制备了单晶铸件,采用ProCAST有限元模拟软件包计算了LMC定向凝固工艺下,不同抽拉速度单晶高温合金铸件定向凝固过程的温度场,预测了拉速对单晶生长缺陷的影响。结果表明,模拟结果与实验结果吻合良好,计算的温度曲线在1100℃以上与实测温度曲线相比误差小于5%;随着抽拉速度的增加,凝固界面下凹,曲率增加,铸件缘板处出现杂晶的倾向增大。
