Protective Coatings for Compressor Gas Path Components

The blades and vanes in gas turbine compressors operating in dusty environments are prone to degradation by solid particle erosion, which causes surface roughening and changes in airfoil geometry. This results in decreased compressor performance, and higher specific fuel consumption, leading to significantly increased operational cost. Erosion damage is more prominent in flight engines without air inlet filter protection. Application of a thin ceramic titanium nitride (TiN) coating to improve the erosion resistance of compressor airfoils was thoroughly investigated. Coatings were applied to engine hardware by a Reactive Ion Coating (RIC) process and optimized to produce a very adherent erosion resistant coating. Computer modeling of the erosion process occurring on coated and uncoated airfoils suggested that the operational life of the compressor can be enhanced by a factor of two. A complete set of compressor blades and vanes for an Allison T56 turboprop engine was coated for engine qualification tests. Laboratory tests showed that the thin coating had no significant influence on either the resonant frequency or the fatigue resistance of the blades and the instrumented engine tests confirmed that the performance was typical of overhauled engines, with no aerothermodynamic loss. Therefore, titanium nitride coatings are suitable for service and can be used on existing engines to improve the life of the compressors.