Original Date: 03/08/1999
Revision Date: 01/18/2007

Fretting and low-cycle fatigue occurs when two surfaces come into contact under pressure with a high frequency of reciprocating motion. This type of fatigue is adversely affecting the compressor and fan sections of the F404 engine in the F/A-18. The current configuration of the titanium fan blade and the titanium fan disk provides for a copper- nickel-indium coating on the blade root. When this coating fails, the top surface material’s properties change and lead to cracking at the interface. If not discovered in time, this wear can lead to catastrophic failure of the compressor section.

The Applied Research Laboratory at the Pennsylvania State University (ARL Penn State) initiated the F/A-18 F404 Engine Fretting and Low-Cycle Fatigue Study to evaluate the failure mechanisms and duplicate them in a laboratory environment. The study has determined fretting and damage modes of current titanium dovetail/disc components for establishing a baseline failure configuration. After establishing this configuration, an optimum coating and/or coating process was developed and implemented at manufacturing facilities and repair depots. This approach has eliminated/minimized fretting and low-cycle fatigue at the blade-disk interface.

A shot peening process for the blades is also being evaluated. Intermetallic layers at the blade root sections have been identified through the study. The presence of this layer occurred from the unexpected diffusion of titanium and copper-nickel-indium coatings, and could cause the failures.

For more information see the Point of Contact for this survey.