温度及加载速率对U-5.7%Nb合金变形行为的影响

研究了淬火和时效2种状态的U-5.7%Nb合金,从室温(20℃)~800℃温度范围的准静态拉伸性能,及合金的变形和断裂行为。结果表明,不论淬火或时效状态的U-5.7%Nb合金,当温度高于200℃后,合金在室温下表现出的二次屈服现象将完全消失,并在400℃温度附近发生脆化,在700℃温度附近表现出明显的超塑性,其中淬火态合金性能的变化尤为明显。并对准静态拉伸、Hopkinson拉伸及爆炸膨胀环3种加载速率下,时效态U-5.7%Nb合金的组织结构进行了对比分析。结果表明,以不同应变速率断裂的时效态U-5.7%Nb合金,断口中心部位的韧窝比边缘部位相对明显,Hopkinson拉伸断口的晶粒大于准静态拉伸断口的晶粒,爆炸速率断裂的合金断口有剪切断裂、边缘开裂及局部夹杂脱落的现象。

Influence of Temperature and Loading Rates on Deformation Behaviors

Quasi-static tensile properties, deformation and fracture behaviors of both quenched and aged U-5.7%Nb alloys in a temperature range from room temperature to 800 oC were investigated. The results show that the second yield phenomenon of both quenched and aged U-5.7%Nb alloys occurring at room temperature disappeared at a temperature higher than 200 oC, and the embrittlement behaviors of two alloys appeared at 400 oC. Meanwhile, the superplasticity has been observed in two alloys at the temperature higher than 700 oC, and the superplasticity of the quenched alloys was more evident than that of the aged alloys. The microstructures of the aged U-5.7%Nb deformed at quasi-static tension, Hopkinson tension and expansion loadings have been analyzed. The results indicate that the dimples at the center zone of the specimens were more obvious than that at the rim zone in aged U-5.7%Nb alloys fractured at different strain rates. And the grains at the fracture of Hopkinson tension were larger than that of the quasi-static loading. Shear fracture, rim cracking and inclusion falling off were observed in the fracture of the alloys deformed at expansion loading