Erosion Characterization of Coated Superalloys in Turbomachinery Applications

The ingestion of suspended particles by high performance turbomachinery reduces engine efficiency and life. New developments in blade coating materials have contributed to compressor and turbine design improvements. A knowledge of the important phenomna associated with material erosion by particulate flow is required in the design. This paper gives an overview of the experimental studies of the erosion characteristics of coated superalloy blades conducted at the University of Cincinnati’s test facilities for blade and coating materials erosion will be described. Results will be presented and discussed for the erosion characteristics of various blade materials and coatings. The investigated coatings are produced via plasma spray, detonation guns, chemical vapor deposition (CVD), and physical vapor deposition (PVD).

Microstructure and Properties of Thermally Sprayed TiC-Ni and (Ti,Mo) C-NiCo Coatings

Hardmetal-like coatings on the base of titanium carbide as a hard phase and nickel as a metal binder were prepared from agglomerated and sintered powders by plasma spray, detonation gun spray and high-velocity oxygen-fuel spray processes. The powders used in the spray experiments were plain TiC-Ni type and alloyed (Ti,Mo)C-NiCo type powders with different binder content. The coatings were characterized by optical and scanning electron microscopy, microhardness measurements, XRD analysis and in an abrasion wear test. The results showed that the sprayability of these novel hardmetal-like powders is good in all spray processes studied and the coatings deposited were found to have dense microstructures and good properties. The XRD analysis showed that the coatings have a phase structure similar to that found in the spray powder. The amount of retained carbides in the coatings was high. Some regions in which the carbides had dissolved with the metallic binder phase during spraying were also found, especially in plasma sprayed coatings. In such microstructural regions submicron size reprecipitated carbides were detected. These were clearly detectable in detonation gun sprayed coatings. HVOF sprayed coatings were found to contain a very high content of retained carbide phase. In this process the heat effect to the material seemed to be the lowest. The wear tests clearly showed the importance of alloying the hard phase and the binder phase in order to improve the wear resistance of the coatings. All studied spray processes produced coatings with nearly similar coating wear properties.