Four castings with different modulus have been designed to simulate different thickness sections of a turbine blade during casting process. The microstructure has been observed by optical microscopy （OM） and scannin...Four castings with different modulus have been designed to simulate different thickness sections of a turbine blade during casting process. The microstructure has been observed by optical microscopy （OM） and scanning electron microscopy （SEM）. The micro-segregation was tested by energy dispersive spectroscopy （EDS） and the macro-segregation was analyzed by using Metalscan 2500 spectrometers. The experimental results show that the microstructure of casting is affected by modulus apparently. The smaller the modulus, the finer the microstructure. The average grain size of castings with modulus of 0.29, 1.57, 3.10 and 5.0 mm is 0.3, 1.5, 2.7 and 4.3 mm, and the volume fraction of eutectic is 0, 0.1%, 0.2% and 1.0%, respectively. The micro/macro segregation is affected by the modulus apparently. The smaller the modulus, the lower the segregation level. When the modulus of casting increases, the content of AI increases, while the content of W, Cr and Mo decreases both in inner grain and near grain boundary. The content of AI and Mo in inner grain is higher than that near grain boundary, while the content of Cr and W in inner grain is lower than that near grain boundary.展开更多
Shrinkage porosity is a type of random distribution defects and exists in most large castings. Different from the periodic symmetry defects or certain distribution defects, shrinkage porosity presents a random "c...Shrinkage porosity is a type of random distribution defects and exists in most large castings. Different from the periodic symmetry defects or certain distribution defects, shrinkage porosity presents a random "cloud-like" configuration, which brings difficulties in quantifying the effective performance of defected casting. In this paper, the influences of random shrinkage porosity on the equivalent elastic modulus of QT400-18 casting were studied by a numerical statistics approach. An improved random algorithm was applied into the lattice model to simulate the "cloud-like" morphology of shrinkage porosity. Then, a large number of numerical samples containing random levels of shrinkage were generated by the proposed algorithm. The stress concentration factor and equivalent elastic modulus of these numerical samples were calculated. Based on a statistical approach, the effects of shrinkage porosity's distribution characteristics, such as area fraction, shape, and relative location on the casting's equivalent mechanical properties were discussed respectively. It is shown that the approach with randomly distributed defects has better predictive capabilities than traditional methods. The following conclusions can be drawn from the statistical simulations:(1) the effective modulus decreases remarkably if the shrinkage porosity percent is greater than 1.5%;(2) the average Stress Concentration Factor(SCF) produced by shrinkage porosity is about 2.0;(3) the defect's length across the loading direction plays a more important role in the effective modulus than the length along the loading direction;(4) the surface defect perpendicular to loading direction reduces the mean modulus about 1.5% more than a defect of other position.展开更多
文摘Four castings with different modulus have been designed to simulate different thickness sections of a turbine blade during casting process. The microstructure has been observed by optical microscopy （OM） and scanning electron microscopy （SEM）. The micro-segregation was tested by energy dispersive spectroscopy （EDS） and the macro-segregation was analyzed by using Metalscan 2500 spectrometers. The experimental results show that the microstructure of casting is affected by modulus apparently. The smaller the modulus, the finer the microstructure. The average grain size of castings with modulus of 0.29, 1.57, 3.10 and 5.0 mm is 0.3, 1.5, 2.7 and 4.3 mm, and the volume fraction of eutectic is 0, 0.1%, 0.2% and 1.0%, respectively. The micro/macro segregation is affected by the modulus apparently. The smaller the modulus, the lower the segregation level. When the modulus of casting increases, the content of AI increases, while the content of W, Cr and Mo decreases both in inner grain and near grain boundary. The content of AI and Mo in inner grain is higher than that near grain boundary, while the content of Cr and W in inner grain is lower than that near grain boundary.
基金supported by the National Natural Science Foundation of China(Grant No.51305350)the Basic Research Foundation of NWPU(No.3102014JCQ01045)
文摘Shrinkage porosity is a type of random distribution defects and exists in most large castings. Different from the periodic symmetry defects or certain distribution defects, shrinkage porosity presents a random "cloud-like" configuration, which brings difficulties in quantifying the effective performance of defected casting. In this paper, the influences of random shrinkage porosity on the equivalent elastic modulus of QT400-18 casting were studied by a numerical statistics approach. An improved random algorithm was applied into the lattice model to simulate the "cloud-like" morphology of shrinkage porosity. Then, a large number of numerical samples containing random levels of shrinkage were generated by the proposed algorithm. The stress concentration factor and equivalent elastic modulus of these numerical samples were calculated. Based on a statistical approach, the effects of shrinkage porosity's distribution characteristics, such as area fraction, shape, and relative location on the casting's equivalent mechanical properties were discussed respectively. It is shown that the approach with randomly distributed defects has better predictive capabilities than traditional methods. The following conclusions can be drawn from the statistical simulations:(1) the effective modulus decreases remarkably if the shrinkage porosity percent is greater than 1.5%;(2) the average Stress Concentration Factor(SCF) produced by shrinkage porosity is about 2.0;(3) the defect's length across the loading direction plays a more important role in the effective modulus than the length along the loading direction;(4) the surface defect perpendicular to loading direction reduces the mean modulus about 1.5% more than a defect of other position.
