Yttria Deposition by a Novel Plasma Torch

Carbon dioxide (CO₂) and hydrocarbons (such as CH₄) gas mixtures generate plasmas with much higher enthalpy and thermal conductivity, leading to higher spray process efficiency and improved heat transfer to the sprayed powder. We have employed a DC plasma torch operated with CO₂+CH₄ gas mixture, which has been developed at the Centre for Advanced Coating Technologies (CACT) at the University of Toronto, to deposit various coatings. This study was focused on the effect of this plasma gas mixture on the in-flight particle parameters during plasma spraying of Yttria (Y₂O₃). The results were compared with a similar coating applied by the SG-100 torch (Praxair) with Ar+He gas mixture. The particulate plume scans show that with the CACT torch, all particles in measured volume were overheated at a distance of 120 mm. Cross-sections through the sprayed coatings were polished and examined under a scanning electron microscope. The dielectric properties of the two coatings were also compared with each other.