Leakage failure analysis of nickel-copper gas-proof material used in traveling-wave tube

With the specific characteristic of well ambient temperature mechanical properties, high temperature strength and corrosion resistance, excellent wear-resistance, easy processing, non-magnetic, the nickel-copper alloys were widely applied on the radio frequency (RF) system of the traveling-wave tube (TWT) [1]. The outstanding performance of the TWT is closely related to its gas-proof material. But abnormal sample of poor vacuum tightness and discoloration (turning black) happened in the process of working. Compared with different samples (normal and abnormal ones), both were observed including microstructure and composition analysis combining with electron microanalysis by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The results showed that manganese segregation at grain boundary in the process of burning hydrogen, oxidation reaction with free oxygen on the surface, and the manganese oxide made the surface of nickel-copper alloy black and weaken the cohesive power inside the grain boundary, which the intergranular fracture and poor gas tightness of the nickel-copper alloys were aroused by them.