Damping Coatings for Gas Turbine Compression System Airfoils

The use of monolithic airfoil structures in static and rotating components such as one-piece integrally bladed rotors (IBR's) in military turbine engines has created an increased risk of high cycle fatigue (HCF). The Phase I SBIR studies recently demonstrated plasma sprayed hard coating concepts that show significantly greater damping than has been observed in previous investigations. Polymer-impregnated plasma sprayed coatings exhibited over 6 times the damping of typical plasma sprayed damping coatings at low dynamic strains and close to twice the damping at higher strains. High-cycle fatigue tests showed only a 10% drop in the maximum tolerable load when compared with specimens with no coating. Phase II efforts will investigate the effect of processing parameters on damping and overall mechanical properties. Studies will also include damping, fatigue, erosion, impact investigations and spin-pit testing of coated airfoils. The development of robotic manipulation programs for robotic plasma spraying of complex shaped prototype blades will provide consistent plasma sprayed coatings. A concerted effort to study a large sample of plasma sprayed damping metal and ceramic coatings in conjunction with the investigation of other viscoelastic materials should provide a significant number of candidate coating systems with exceptional damping properties over a wide temperature range.