Measurement of a Low Power Plasma Jet by the Enthalpy Probe

The effects of the plasma gas composition (Ar-N₂, Ar-H₂), arc current and voltage on the temperature and velocity of a low power (5 kW) plasma torch in the arc field free region have been investigated using an enthalpy probe. Coatings of Al₂O₃-13TiO₂ were deposited under different conditions. The results show that in the Ar-N₂ plasma, the enthalpy, temperature and velocity change little with arc current and voltage when regulating the nitrogen proportion in the plasma gas, and the hardness of the resulting coatings is 800-900 HV. For Ar-H₂ plasma, however, increasing the H₂ content in the gas mixture remarkably enhanced the velocity and heat transfer of the plasma jet with the result that the coatings showed the high hardness up to 1200 HV.