Homogeneous arc ablation behaviors of CuCr cathodes improved by chromic oxide

doi:10.1016/j.jmst.2020.10.083

Abstract

Abstract:

Cathode ablation is one of the dominant limitations for extending the maximum operating time of arc heaters. In this work, the arc ablation behaviors and mechanisms of commercial CuCr10, CuCr25, and CuCr50 cathodes were investigated for pure copper and pure chromium cathodes. The discharging homogeneity was improved with the increase of chromium content in the cathodes, which was attributed to the formed chromic oxide layer. The CuCr50 cathodes exhibited the lowest ablation rate with a reduction of 27.0% compared to the copper cathodes. The chromic oxide formed in the pit protected the bottom matrix, leading to a homogeneous ablation process. The mechanism for the improved homogeneous ablation behaviors of the CuCr50 cathodes was proposed and featured by the suppression of deep pits and the dispersion of arc foot. Future attention will be focused on designing composite cathodes with an anti-ablation surface layer and a good conductive matrix.

Key words: Arc ablation, CuCr cathodes, Chromic oxide, Microstructure

Weimian Guan, Jie Yuan, Hao Lv, Tao Zhu, Youtong Fang, Jiabin Liu, Hongtao Wang, Zhihui Li, Zhigong Tang, Wei Yang. Homogeneous arc ablation behaviors of CuCr cathodes improved by chromic oxide[J]. J. Mater. Sci. Technol., 2021, 81: 1-12.

Figures/Tables 12

Table 1 Electrical and mechanical properties of CuCr alloys.

Alloys	Electrical conductivity (%IACS)	Hardness (HB)	Density (g cm^-3)
CuCr10	65.8 ± 1.3	76.9 ± 3.2	8.70
CuCr25	57.5 ± 2.4	86.8 ± 4.7	8.38
CuCr50	36.7 ± 3.0	117.2 ± 4.1	7.96

Fig. 1. Microstructures of the commercial (a) CuCr10, (b) CuCr25, and (c) CuCr50 cathodes.

Fig. 2. 3-D morphologies, top views, and cross-section profiles of the ablated (a, b) copper, (c, d) CuCr10, (e, f) CuCr25, (g, h) CuCr50, and (i, j) chromium cathodes.

Fig. 3. (a) Maximum ablation depths of the cathodes discharging for 240 s. (b) Curves of ablation rate and discharge time. The insets in (a) correspond to the cross-section profiles of the cathodes discharging for 240 s.

Fig. 4. Surface microstructures of the ablated areas in (a) copper, (b) CuCr10, (c) CuCr25, (d) CuCr50, and (e) chromium. The insets in (a) and (b) display the observed craters or pits. The areas circled by yellow dashed lines in (b) correspond to the scattered discharging areas.

Fig. 5. Cross-section microstructures of (a) copper, (b) CuCr10, (c) CuCr25, (d) CuCr50, and (e) chromium discharging for 240 s. The inserted Table 2 displays the compositions of the selected areas in (b), (c), and (d).

Fig. 6. Ablation craters or pits in (a) copper, (b) CuCr50, and (c) chromium ablated for 240 s.

Fig. 7. Surface morphologies and microstructures of (a) CuCr10, (c) CuCr25, and (e) CuCr50 cathodes with a discharging time of 3 s. The images in (b), (d), and (f) magnified the ablation pits in the corresponding cathodes.

Fig. 8. Energy dispersive spectroscopy (EDS) mappings of the pits in (a) CuCr10 and (b) CuCr50 discharging for 1 s. Graphs (c), (d) correspond to the EDS mappings of the whole selected areas in (a) and (b), respectively.

Fig. 9. Evolutions of the crater-like structures in (a-c) CuCr10, (d-f) CuCr25, and (g-i) CuCr50 cathodes with a discharging time of 1 s to 5 s. Graphs (j) and (k) display the craters in copper and chromium discharging for 5 s. (l) Curves of the pit diameter and the arc ablation time.

Fig. 10. Captured sequential images of discharging in (a-d) CuCr10, (e-h) CuCr25, and (i-l) CuCr50 cathodes. Full details of the cathode spot motion behaviors are given in movies a-c in the Supplemental Material.

Fig. 11. Schematics of the ablation mechanisms of (a-c) CuCr10 cathodes and (d-f) CuCr50 cathodes.

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