Development of a Nonmetallic Abradable Material System for Gas Turbine Applications

Abstract

The performance of gas turbine engines is highly dependent upon the clearance between compressor rotating blades or stator vanes, and adjacent shrouds. Auxiliary power units (APU) incorporate abradable coatings on compressor shrouds to allow for very small clearances and rub tolerance. The operating environment of the APU may result in a combination of abrasion between airfoil tips and shrouds, as well as galvanic corrosion of the abradable material. Experience has shown that established thermal spray abradable material systems that offer desirable abradability properties in laboratory testing may perform poorly when subjected to a combination of galvanic corrosion and abradable environment. This paper discusses development and evaluation of an abradable material that is composed of nonmetallic constituents. This material is not susceptible to galvanic corrosion, and maintains its abradable properties when operating in a combined corrosive and abradable environment. The material development, microstructure, and physical properties are discussed. In addition, the performance of the material in abradability testing, and warm salt fog testing is presented.