Arc-ultrasonic Effect And Property Optimization In Plasma Spraying Of TBCs

ZrO₂ thermal barrier coatings (TBCs) are important in aero-industry applications. Plasma spaying is a main method to form TCBs. Based on the plasma spraying process of TBCs, the effect and optimization of qualities of TBC in plasma spraying by arc-ultrasonic was investigated. Compared with the coatings without ultrasonic, the microstructure and performance of the coatings under ultrasonic were studied to find the effect of arc-ultrasonic. The exciting mechanism and effect of ultrasonic in the plasma spraying process were discussed briefly in this paper.According to the characteristics of TCBs, the thickness of the coating, the adhesive strength of the coating, the thermal shock performance and the microstructure were chosen to be the standards of the coating quality test and evaluation. Experiments were devised by using the plasma spraying system, the arc-ultrasonic exciting system and the signal examining system so as to get comprehensive and integrated results.The influences of arc-ultrasonic frequency and current on the qualities of TBC were investigated. Compared with the coatings without ultrasonic, the thickness of coatings with arc-ultrasonic increases prominently under the same condition of spraying. The adhesive strength of most of the coatings increases and the most prominent ones can increase by more than 20%. The data of adhesive strength are much more concentrative. All TBCs specimens with different arc-ultrasonic frequency have better performance in the thermal shock test. And coatings on some specimens with certain frequency can bear about 50% more thermal cycles than coatings without arc-ultrasonic. The porosity and cracks of ZrO₂ coating decrease when arc-ultrasonic is induced and the porosity and cracks are uniformly distributed. The coatings become more compact under arc-ultrasonic. The frequency parameters of 50kHz and 80kHz and the current parameter of 10A are the most effective to the improvement of the TBC qualities.Based on the tests of the TBC qualities, the exciting mechanism was probed into. The excited ultrasonic improves the heating efficiency of powder and changes the distribution and property of residual stress in the coatings. So the performances of coatings are improved. The signal examining system was used to test the ultrasonic pressure in the plasma spraying process. The result shows that the transfer of energy in the process meliorates under the effect of arc-ultrasonic.The result of the dissertation is valuable to the practical use of the plasma spraying by arc-ultrasonic.