Understanding the Impact of Binary Plasma Gas Mixtures in Plasma Spraying

In plasma spraying, H2 or N2 is commonly added to the primary Ar plasma which may increase the specific enthalpy, thermal conductivity and thus improve the process efficiency. The objective of this study is to provide a process characterization of a three-cathode plasma torch with various binary gas compositions. Several process diagnostics are used to characterize the impact of binary plasma gas mixtures in plasma spraying. High-speed video analysis is utilized to capture the jet fluctuations of the studied process parameters. In addition, current and voltage measurements are performed to further complement the plasma diagnostics. The impact of the binary plasma gas mixtures is determined using particle diagnostic system DPV-2000 by measuring the particle in-flight properties of Al2O3 feedstock. Furthermore, the deposition efficiency (DE) of the investigated process parameters is determined. The results show that at the identical volumetric flow rate and current, the addition of H2 yields the highest particle temperatures, followed by Ar/N2 mixtures and pure Ar plasma. In reverse order, pure Ar plasma results in the highest particle velocities. In addition, the increased DE of plasma spraying with binary gas mixtures for Al2O3 coatings offers the potential to increase the deposition rate of other ceramic materials. This study provides a comprehensive correlation between plasma and particle diagnostics and the deposition efficiency of binary plasma gas mixtures.

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Key words: alumina, deposition efficiency, gas compositions, particle in-flight properties, plasma spraying, plasma torches

Originally published as ITSC2024 Thermal Spray Proceedings online paper (Paper No: itsc2024p0689, pp. 689-695; 7 pages)
By K. Bobzin, H. Heinemann, M. Erck, K. Jasutyn