No abstract

Ceramic matrix composites (CMCs), especially SiC/SiC, have garnered significant attention owing to their remarkable mechanical properties at higher temperatures. For protection of the substrate from oxidation, the SiC/SiC CMCs inherently require environmental barrier coating (EBC). Because aeroengines must function under a wide range of conditions and environments, the coated CMC must be sufficiently resistant to various damage modes. Among these, the effect of microparticles is one of the limiting factors for durability and performance of components, particularly when the engine is operated in dusty areas. The main goal of this experimental research is to investigate and determine the surface damage behaviour of the coated CMC caused by micro sand particles. The data were surveyed across a fairly broad range of exposed temperatures and velocities, and covered conditions relevant to advanced hot section designs. In the experiments, silica or alumina sand entrained in the gas stream was jet-blasted from the nozzle and then impinged on the target CMC+EBC coupon. Owing to the broad testing range, the damage mode and extent of damage varied considerably by condition. The obtained data were then reorganised and compared with several previously proposed particle impact models. This is to first understand and obtain a complete picture of all the probable consequences in the expected design and off-design conditions, and second, to determine the validity of, and deviations from the conventional modelling with the present CMC+EBC material, which will be useful in the next component design phase.

Novel underfill resins combining a thermoset epoxy resin with thermoplastic polyester resins have been developed for self-organization soldering. Polyester-modified epoxy resins, which are hybrid resins, exhibited minimal viscosity at the melting point of the Sn58 mass%Bi solder, with the viscosity dependent on the content and molecular mass of the blended polyester resin. Because the epoxy resin was sufficiently compatible with the polyester resin in the hybrid, the curing reaction of the hybrid resin was similar to that of the epoxy resin. The chemical structure of the polyester resin was retained in the cured hybrid resin, imparting thermoplasticity to the hybrid resins cured with repeated heating. Successful self-organization soldering was achieved using the developed hybrid-resin-based solder paste. [

Ceramic matrix composite (CMC) has better durability at high temperature and lower material density, as compared to nickel-based superalloys 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 a 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 has not 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 a turbine cascade under particle-laden hot gas stream. In the present work, erosion tests were first carried out in a testing facility with an erosion media of 50 μm silica sand. The tests were conducted under a flow velocity of 225 m/s and a temperature of 1311 K to simulate typical aero-engine conditions, and impact angles of 30, 60, and 80 deg 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.