Parametric Appraisal of Slurry-Sprayed Mullite Coatings for Coating Thickness

The slurry spray technique (SST) has been employed to deposit mullite-based coatings on ASTM 1018 low-carbon steel substrate for environmental barrier coating applications. A Taguchi L-18 orthogonal array is adopted for optimization of the identified process variables and material parameters, namely stamping pressure, fly-ash content, and sintering additive, time, and temperature. The measured thickness of the produced coatings was chosen as the response characteristic for the present study. The optimum values of the process variables were predicted by employing analysis of variance based on raw data and the signal-to-noise (S/N) ratio. Based on analysis of the experimental results, the effect of each parameter level on the coating thickness is discussed. It is observed that the sintering temperature had a strong influence on the maximum coating thickness of the slurry-sprayed coating. The as-sprayed coatings fabricated using SST demonstrated splat morphology with continuous interface, suggesting good adherence to the substrate.