Erosion Testing of Environmental-Barrier-Coated CMC and its Behavior on an Aero-Engine Turbine Vane Under Particle-Laden Hot Gas Stream

Abstract

Ceramic matrix composite (CMC) has better durability at high temperature and lower material density, as compared to nickel-based super-alloys which have been the standard material for hot section components of aero-engines. Among the CMC materials, SiC-SiC CMC is especially promising with its superior mechanical property at higher temperature. It, however, inevitably needs environmental barrier coating (EBC) to protect the substrate against oxidation. The EBC also needs to have other functions and to meet various requirements. One such very critical requirement is the resistance to sand erosion, although the issue hasn’t been investigated well so far. The primary contribution of this work is to reveal the erosion resistance of the CMC+EBC material with wind tunnel test data of good quality and to demonstrate what erosion behavior the material exhibits in turbine cascade under particle-laden hot gas stream. In the present work, erosion tests were first carried out in a testing facility with erosion media of 50 microns silica sand. The tests were conducted under flow velocity of 225 m/s and temperature of 1311 K to simulate typical aero-engine conditions and impact angles of 30, 60, and 80deg were investigated. The obtained data showed a typical brittle erosion mode, where the erosion rate had a positive dependence on the impact angles. A typical erosion model, Neilson-Gilchrist model, was applied to correlate the data and the model was shown to have a good agreement with the experimental data once it was properly calibrated. Then, the numerical computation solving particle-laden flow was carried out to predict three dimensional flow field and particle trajectories across the target turbine cascade. The erosion profile along the airfoil was calculated based on the obtained trajectories and the calibrated erosion model. The trajectories showed that the particles mostly impinged the airfoil pressure surface first and then the rebounded particles attacked the opposite suction surface as well. Accordingly, the predicted erosion profile showed a broad erosion band across the pressure surface and also some slight erosion peak at around the mid-chord of the suction surface.