束流偏移对钒合金与不锈钢电子束阻隔熔化焊接头性能的影响

以金作为中间层采用电子束阻隔熔化焊方法来实现V-5Cr-5Ti钒合金与HR-2不锈钢之间的连接,研究电子束流的偏移对接头性能的影响.结果表明,不偏移电子束流(偏移距离d=0)焊接得到的钒合金与不锈钢接头界面将产生贯穿性裂纹,直接导致焊接失败.通过电子束流的偏移(偏移距离d等于束斑半径)一定程度降低了结合界面金属间化合物的产生,实现了钒合金与不锈钢的冶金结合.金作为中间层添加元素,很好地抑制了V/Fe界面的金属间化合物的产生,显著提高了接头性能,接头抗拉强度超过380 MPa.钒合金/不锈钢异种金属焊接接头焊缝正反面成形良好,X射线探伤未发现裂纹和气孔缺陷.

束流偏移量对IC10/GH3039电子束焊接头成型及性能的影响

对航空发动机整体叶盘所采用的GH3039高温合金和IC10镍基单晶高温合金进行了电子束对接实验，IC10单晶高温合金与GH3039高温合金母材成分上的差异以及两侧熔化量不同，导致焊缝中各元素比例变化，使得接头力学性能出现差异。因此，通过电子束偏束流焊接来控制焊缝区各母材熔化量，来改善接头的力学性能。分析了光束偏移对接头力学性能的影响及典型接头横截面的组织特征，综合分析了光束偏移对焊缝微观硬度影响。结果表明，焊缝横截面未见裂纹、气孔等缺陷，焊缝上下宽度相当，最宽处达到1．8mm左右，中心熔宽在0．8mm左右，呈典型的“I”形，并以电子束作用中心为基准对称分布，焊缝组织主要由两侧的枝状晶及中心的等轴晶组成；接头的显微硬度从GH3039侧经焊缝到IC10侧呈逐渐递增趋势，W和Co元素的固溶强化、γ’强化相的含量的增加、晶粒粗化是显微硬度七升的原因，其中最高硬度可以达到HV450。

Flow-Induced Acoustic Resonances in Exhaust Gas Economizer Tube Banks

To investigate the conditions under which acoustic resonances occur, staggered arrays of closely spaced rigid tubes were tested in a wind tunnel under various flow velocities. The author investigated the Strouhal numbers at which flow periodicities occur, the relation between these Strouhal numbers and those at which acoustic resonances occur, and the effects of Reynolds number and longitudinal tube spacings on the occurrence of acoustic resonance. This investigation showed the following： （1） Acoustic resonance can be produced at a frequency well removed from that of vortex shedding. The results also show evidence of vortex shedding and acoustic resonance existing simultaneously but at different frequencies. （2） Acoustic resonance behavior is consistent with that of a self-excited system. （3） A new model of this phenomenon provides an improved procedure for avoiding acoustic resonances in closely spaced tube banks.