Abstract
From the literature, it is known that due to their glass formation tendency, it is not possible to deposit fully-crystalline silicate coatings when the conventional atmospheric plasma spraying (APS) process is employed. In APS, rapid quenching of the sprayed material on the substrate facilitates the amorphous deposit formation, which shrinks when exposed to heat and forms pores and/or cracks. This paper explores the feasibility of using a high-velocity oxygen-fuel (HVOF) process for the cost-effective fabrication of dense, stoichiometric, and crystalline Yb2Si2O7 environmental barrier coatings. We report our findings on the HVOF process optimization and its resultant influence on the microstructure development and crystallinity of the Yb2Si2O7 coatings. The results reveal that partially crystalline, dense, and vertical crack-free EBCs can be produced by the HVOF technique. However, the furnace thermal cycling results revealed that the bonding of the Yb2Si2O7 layer to the Silicon bond coat needs to be improved.
Highlights
Silicon carbide (SiC) fiber reinforced SiC ceramic matrix composites (CMCs), having a relatively low density and higher temperature capability compared to their metallic superalloy counterparts, are notable materials for the future of gas turbine engine technology
The high-velocity oxygen-fuel (HVOF) process was used for the deposition of the Yb2Si2O7 coatings, and the effects of the
The concurrent changes in the area specific weight and arithmetic mean roughness associated with the presence of molten/non‐molten particles in the coatings at different process associated with the presence of molten/non-molten particles in the coatings at different process conditions were interpreted
Summary
Silicon carbide (SiC) fiber reinforced SiC ceramic matrix composites (CMCs), having a relatively low density and higher temperature capability compared to their metallic superalloy counterparts, are notable materials for the future of gas turbine engine technology. Modification in the plasma spraying process was proposed, suggesting the utilization of a furnace in which the substrate to be deposited is placed and heated up to 1200 ◦ C [15] By this adjustment, the deposition of dense and crystalline RE-silicate coatings was found to be ensured, yet, secondary phases in the coatings as a result of the evaporation of Si-containing species could not be avoided [16]. In a recent study [17], it was reported, based on initial trials, that the HVOF process can be an alternative method to achieve dense Yb2 Si2 O7 coatings with desired properties This is because, in contrast with the APS process, HVOF offers a low heat transfer to the particles (flame temperatures up to 3000 ◦ C), reducing the molten fraction of the sprayed powders which is expected to be favorable for obtaining crystalline and stoichiometric coatings.
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