Cathode erosion hinders the development of high-power arc heaters, and the inhomogeneous erosion of the copper cathode results in catastrophic failures. In this work, the arc erosion behavior of a chromium cathode was investigated compared with copper. The former was relatively homogeneous with shallow erosion pits. The eroded microstructure suggests that the surface chromic oxide layer could suppress the formation of deep craters. The maximum erosion depth and the erosion rate of chromium were lower than those of copper. The single erosion pits on chromium gradually extended and disappeared, suggesting a reduction in the input energy flux density. The underlying mechanism for the homogeneous erosion behavior of the chromium cathode was proposed. The homogeneous erosion behavior of the chromium cathode makes it a promising candidate for high-power arc heaters.
Discharge homogeneity is one of the dominant factors affecting cathode lifetime. In this work, the arc ablation behavior of a zirconium cathode is investigated in air and argon atmospheres. Homogeneous discharge processes are observed in air, while poor discharge homogeneity with scattered cathode spots is found in argon. The homogeneous discharge process is related to the layered structure at the discharge center. The surface zirconium oxide layer stabilizes the arc foot and reduces the effective work function. A dual-phase layer underneath, consisting of zirconium oxides and zirconium, enables the transition from the zirconium matrix to the surface oxide layer. The sustainable discharge behaviors are realized by the balance in the cathode, which is created by the ablation of surface zirconium oxides and the oxidization of zirconium in the dual-phase layer.
Arc ablation threatens the cathode operating time and restricts the development of high‐power arc heaters. Surface modification is an effective strategy in improving cathode ablation resistance without reducing matrix conductivities. Herein, Nb layer and Ti layer are laser clad on Cu matrix to decrease the arc ablation of Cu cathode. The total thickness of laser‐clad Nb/Ti layer reaches 1850 μm. The Nb layer restrains Cu from diluting into surface cladding and no detrimental Ti–Cu intermetallic is formed. The surface Ti content is as high as 98.34 at%, guaranteeing the arc discharge homogeneity. The arc ablation behaviors of Ti/Nb/Cu cathodes are investigated in air atmosphere. The layered cathode discharges and ablates homogeneously. The arc discharge center is shallow with no appearance of deep pits or craters. The maximum ablation depth (72.1 μm) after 30 s discharging is ≈33.4% lower than that of Cu cathode. Besides, the cathode ablation rate, 1.61 μg C−1, is ≈27.5% lower than Cu cathode. The improved arc ablation resistance is interpreted in the protective effect of refractory TiO2 layer formed during air arc discharging.
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