Effect of Different Cathode Materials on PS-PVD Plasma Jet

The work aims to explore the effect of hot cathode materials on advanced plasma spraying physical vapor deposition (PS-PVD) jet. Cerium tungsten, thorium tungsten and lanthanum tungsten materials were used to prepare high-power plasma spray torch cathodes, and the coatings were prepared under the same process conditions. The optical emission spectrometer (OES) was used to detect the spectral intensity of plasma jet under the conditions with and without powder feeding. The energy field distribution and stability of plasma jet were evaluated respectively, and the microstructure of the coatings was analyzed by scanning electron microscope. Under the condition of no powder feeding, the intensity of ArⅠand He Ⅰcharacteristic peaks in the plasma jet with lanthanum tungsten cathode was the highest between 400 mm and 1 000 mm, and decreased significantly after 1 000 mm. When thorium tungsten cathode was used, the intensity of ArⅠcharacteristic peak in the axial center gradually increased to 1 000 mm, then decreased slowly, and the intensity of HeⅠcharacteristic peak decreased rapidly. When cerium tungsten cathode was used, from 600 mm to 1 200 mm, the intensity of ArⅠcharacteristic peak decreased most slowly, and the intensity of HeⅠcharacteristic peak gradually increased. The fluctuation of plasma jet was cerium tungsten > thorium tungsten > lanthanum tungsten. In the powder feeding state, in the peak intensity region, the spectral intensity of different elements in thorium tungsten cathode excited plasma jet was the highest, and the spectral intensity of lanthanum tungsten and cerium tungsten cathode excited plasma jet was close. Above the plasma jet axis, the spectral intensity of cerium tungsten cathode was the highest. In the high concentration gas phase region, the coating prepared by thorium tungsten cathode was mainly deposited in high gas phase ratio, and the dendrite growth was developed. A large number of gas phase condensation nano-particles and a certain amount of droplet condensation spherical particles appeared between the coating columns prepared by cerium tungsten and lanthanum tungsten cathodes. The plasma jet generated by lanthanum tungsten cathode has the highest energy intensity and the best plasma jet stability in the axial range of 400~1 000 mm, but there is a large axial and radial (HeⅠ) energy attenuation after 1 000 mm. Considering the optimal spraying distance ≤1 000 mm, when the deposition distance is 1 200 mm, there are more spherical condensate particles in the coating deposited by lanthanum tungsten cathode. The energy intensity and stability of the jet generated by the thorium tungsten cathode in the axial 400~1 000 mm region are lower than those of the lanthanum tungsten cathode, but the energy intensity of the plasma jet greater than 1 000 mm decays slowly. The prepared coating exhibits good gas phase diffusion deposition characteristics at different radial positions of the plasma jet in the three cathodes. The plasma jet generated by the cerium tungsten cathode has the smallest energy intensity attenuation between 600~1 200 mm in the axial direction, and a wide range of energy and gas phase distribution characteristics show in both axial and radial directions, but the plasma jet stability is insufficient. © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.