Suspension HVOF Sprayed Ytterbium Disilicate Environmental Barrier Coatings

Environmental barrier coatings (EBCs) are needed to protect Si-based ceramic matrix composites from oxidation and corrosion in gas turbine engine environments. One of the key requirements for a successful EBC application is a dense and crack-free coating. This provides an effective barrier against diffusion of oxidants. In this study, the suspension HVOF (SHVOF) process was utilized for the deposition of Yb2Si2O7 coatings. The effect of the standoff distance on coating microstructure was evaluated. Overall, increased standoff distances lead to higher coating porosity. The phase composition and microstructure of the dense SHVOF Yb2Si2O7 coatings obtained at short standoff distances were characterized using scanning electron microscopy (SEM) and x-ray diffraction (XRD). XRD analysis showed that the as-sprayed dense coating is highly amorphous, and it transformed to crystalline Yb2Si2O7 and Yb2SiO5 phases after 1300 degrees C heat treatment in air. Oxidation behavior of the SHVOF EBCs was investigated and was compared with the typical air plasma sprayed EBCs in flowing 90% H2O(g) + 10% air at 1316 degrees C. The results showed that the thermally grown oxide growth rate of the SHVOF EBCs is over three times slower than that of air plasma sprayed EBCs under the same test conditions.

Automated summary

In this study, Yb2Si2O7 coatings were deposited on Si-based ceramic matrix composites using the suspension HVOF process. The effect of standoff distance on coating microstructure was evaluated, and it was found that shorter standoff distances resulted in denser amorphous coatings transforming to crystalline phases after heat treatment. Furthermore, the oxidation behavior of the SHVOF EBCs was compared with air plasma sprayed EBCs and showed a slower oxide growth rate.