High temperature abradable sealing coating for SiCf/SiC ceramic matrix composites

A study of porous YSZ abradable sealing coating (ASC) plasma-sprayed onto SiCf/SiC ceramic matrix composites (CMC) through the compatibility of intermediate layers is reported. The multilayer Si/Yb2Si2O7/LaMgAl11O19 thermal-environmental barrier coating (T-EBC) is served as intermediate layers in consideration of its ability to protect the CMC from recession and ease the misfit of the thermal expansivity. Isothermal exposure and thermal shock tests were conducted at 1200 degrees C and led to the decomposition of t'-ZrO2 phase to t-ZrO2 and c-ZrO2 phases in YSZ topcoat, the formation of mud-cracks throughout the entire coating structure and thermally grown oxide (SiO2), with following an Yb2Si2O7 reaction layer. The measured bond strength of the coated samples was 5.47 +/- 0.85 MPa, and the fracture position mainly happened inside the CMC substrate. The Superficial Rockwell Hardness (HR15Y) considered to be an important factor in abradability increased by only 1.34% after 1200 degrees C isothermal exposure for 100 h, showing excellent high temperature hardness stability. The abradability of the ASC was investigated by a sliding wear test, the fatigue wear mainly occurred in worn scar when encountering Si3N4 ceramic ball with high hardness and low thermal conductivity, while adhesive wear occurred when GCr15 steel ball with low hardness and high thermal conductivity are encountered.

Automated summary

The study focuses on the compatibility of intermediate layers for the plasma-sprayed porous YSZ abradable sealing coating (ASC) on SiCf/SiC ceramic matrix composites (CMC). Through isothermal exposure and thermal shock tests at 1200 degrees C, the YSZ topcoat experienced decomposition, formation of mud-cracks and thermally grown oxide, along with the reaction layer of Yb2Si2O7. The coated samples exhibited a bond strength of 5.47 +/- 0.85 MPa and showed excellent high temperature hardness stability with a minimal increase in Superficial Rockwell Hardness (HR15Y) after 1200 degrees C isothermal exposure. The abradability of the ASC was influenced by the hardness and thermal conductivity of the encountered balls.