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681.
682.
LIAO Jinge LI Chengxing ZOU Wenbing KANG Jing SONG Jiangfeng JIANG Bin ZHAO Hu YANG Zhiyuan PAN Fusheng 《上海航天》2022,39(1):92-101
Mg-Gd-Y-Zr alloy castings are widely used in the aerospace field owing to their high strength and excellent creep resistance. The castability of these alloys is also an important consideration for engineering application. Thus, the hot tearing susceptibilities (HTSs) of Mg-10Gd-1Y-1Zn-0.5Zr (VW91) alloy and Mg-10Gd-2Y-1Zn-0.5Zr (VW92) alloy are investigated with a constrained rod casting (CRC) mold. The microstructures and fracture surface are characterized by optical microscope and scanning electron microscope. The results unveil that the HTS of VW92 alloy is lower than that of VW91 alloy. The microstructures indicate that obvious tears can be observed in VW91 alloy, while the tears in VW92 alloy are tiny. The tear feeding and healing by eutectic are also observed in VW91 and VW92 alloys. Therefore, the lower hot tearing susceptibility of VW92 alloy is mainly attributed to the high amount of eutectic which feeds and heals tears. Besides, the effects of the coefficient of thermal expansion (CTE) and the fluidity of VW91 and VW92 alloys on their HTSs are discussed. 相似文献
683.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(1):298-305
We present an analysis of the response of quasi-10-day waves (Q10DWs) to the sudden stratospheric warming (SSW) event which occurred on March 23, 2020. The Q10DWs are observed in the mesosphere and lower thermosphere (MLT) region by three meteor radars, which are located at middle latitudes along the 120°E meridian from Mohe (MH, 53.5°N, 122.3°E), Beijing (BJ, 40.3°N, 116.2°E), to Wuhan (WH, 30.5°N, 114.6°E). The Q10DWs reveal similar temporal and altitudinal variations during the SSW in the MLT region at the three stations. The activities of Q10DWs are also captured in the temperature measurements from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite in the MLT region. Further analysis of the Q10DW phases indicates that the Q10DWs might be in situ generated due to mesospheric instabilities at higher latitudes around MH and then propagate southward to lower latitudes at BJ and WH. The atmospheric instabilities are not directly responsible for the excitations of Q10DWs at lower latitudes, while the observed equatorward propagation of the Q10DWs is important. Our result provides the observational evidence for latitudinal couplings in the MLT region after the SSW onset, which is achieved by southward propagating planetary waves in the MLT region. 相似文献
684.