Abradable Coatings for Turboprop Engines

For the engines used in small turboprop aircrafts, introduction of abradable coatings represents a feasible way to reach higher levels of performance by improving the fuel efficiency and increase the temperature margin. Abradable coatings on seals also contribute to improved hot restarts capability of an engine and lead to substantial extension of service life of the rotating counterbodies. Innovated concept of a turboprop engine with abradable coatings in cold, intermediate and hot sections of turboprop will be presented. We will demonstrate how the advanced in-situ measurement techniques can be employed to optimize the abradable coatings design for clearance control in compressor and in generator turbine of an 800 SHP turboprop engine with reverse flow of air and gas. The existing turbine temperatures are in excess of 1600 F and call for employment of ceramic abradable coating with microstructure and properties fine-tuned to balance erosion resistance and suitable level of abradability. Thermal spray process maps and results both from abradable rig tests and engine tests will be presented to illustrate the path for the selection of optimal coatings on various engine parts.