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K417 superalloy castings with different addition of rare earth element Y were produced by vacuum induction melting technology using Y 2 O 3 crucibles under different vacuum degrees. The effects and interaction mechanisms of Y and vacuum degree on the purification of the superalloy were investigated. The results showed that high purification of K417 superalloy with 4∼5 ppm O and N was obtained after addition of Y. There was a characteristic transition during the deoxidation and denitrogenation of the superalloy when the vacuum degree changed. With the addition of 0.5 wt% Y in the alloy, the concentration of O could be reduced from 34 ppm to 8 ppm in rough vacuum and from 13 ppm to 4 ppm in high vacuum, respectively. High vacuum enhanced the chemical dissolution of Y 2 O 3 crucible. The concentration of N decreased from 43 ppm to 14 ppm with the addition of Y in rough vacuum condition of 100Pa. Whereas, in high vacuum condition of 0.035Pa, the concentration of N tend to increase from 4 ppm to 7 ppm. The effect of deoxidation of Y promoted the process of denitrogenation. [ABSTRACT FROM AUTHOR]

The existing methods for optimizing search performance of phased array radar are mainly referred to two parameters, the dwell time of a search beam and the scan time. But for alert-confirm operation mode, the expending time resulting in false alarm is also a factor which affects search performance. The influence on search performance caused by the dwell time of a search beam, scan time and false alarm probability was analyzed, then the optimal operation parameters for search performance was designed. Compared with other methods, the simulation results show the validity of this method. [ABSTRACT FROM AUTHOR]

The effect of La addition (0, 0.1, 0.2, 0.4, wt.%) on the microstructure, tensile properties and fracture behavior of Al-7Si alloy was investigated systematically. It is found that the La appears in the Al-7Si alloy in the form of Al4La and Al2Si2La phases. La addition can refine the secondary dendrite arm spacing (SDAS) and eutectic Si particles, which are decreased by 7.9% and 7%, respectively, with the optimal La content of 0.1wt.%. Because when 0.1wt.% La is added, a relatively higher nucleation undercooling of 37.47 °C is observed. Higher undercooling degree suggests that nucleation is accelerated and subsequent growth is restrained. After T6 heat treatment, compared with the without La, the ultimate tensile strength of the alloy with 0.1wt.% La is enhanced by 5.2% from 333 MPa to 350.2 MPa and the elongation increases by 73% from 7.37% to 12.75%, correspondingly. The fracture mode evolves from the ductile-brittle mixed fracture to ductile fracture mode. However, when La element content reaches a certain value of 0.4wt.%, serious segregation takes place during the solidification process. The formed brittle phases deteriorate the tensile properties of the alloy and the fracture mode of Al-7Si-0.2/0.4 La changes to mixed ductile-brittle fracture mode. [ABSTRACT FROM AUTHOR]