The influence of temperature on the wear mode and deterioration of coatings used for titanium aircarft engine components

The interface between titanium compressor blades and rotors of jet engines was studied to determine the mechanisms responsible for problematic deteriorations of protective Cu-Ni-In coatings. Results indicated that at operational temperatures of 221 C, titanium from the uncoated disk was transferred to the softer Cu-Ni-In coating on the blade. This in turn created titanium on titanium contact and resulted in fretting wear. At higher temperatures of 454°C. copper segregation appears to be the dominant deterioration mechanism. In order to simulate these wear modes and evaluate candidate coatings, a unique testing procedure was developed that included a range of gross-slip scale displacements. Cobalt, molybdenum, tungsten carbide, and Nickel-based coatings were evaluated by this testing procedure that first involved a low-cycle series of gross-slip displacements (125 μm), followed by a higher cycle series in a reduced (25 μm) gross-slip regime. Results of the study revealed that an unlubricated pure-cobalt coating could protect the blade without damaging the disk at elevated temperatures. While no coatings performed exceptionally at lower temperatures, pure molybdenum exhibited some promise.