Abstract

The plasma spraying electrodes are spare parts playing an important role in the process. In order to ensure good coating properties, they have to be frequently replaced. The purpose of this work was to evaluate the electrode lifetime and to study its evolution for different plasma gas (Ar/H2 mixture or SPRAL22) and impurity levels (oxygen and humidity). For these experiments, a PTF4 torch was used. The evolution of the voltage versus time was recorded during spraying. The time elapsed for a 5V drop was taken as the electrode lifetime. Experiments pointed out that the SPRAL22 led to an increase of lifetime by a factor 3 to 4. The evolution of the voltage versus time was also carried out for an Ar/H2 mixture with different oxygen and humidity contents. These impurities were systematically analysed during the tests. The electrode lifetime was strongly affected by both elements. This emphasized the importance of the gas purity in the plasma spraying process.

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