P. J. Golden, Air Force Research Laboratory, Wright-Patterson AFB, OH; A. Hutson, University of Dayton Research Institute, Dayton, OH

Summary:

Fretting can be a significant problem in aerospace structures such as the attachment between blades and disks in turbine engines. Fretting in these dovetail or fir tree attachments is a significant maintenance burden for operators of gas turbine engines. The objective of this work was to investigate the performance of several coatings and surface treatments applied to Ti-6Al-4V specimens and pads subjected to fretting fatigue. Five coating systems were initially chosen and tested using two different fretting fatigue apparatus and also a reciprocating fretting setup. The five coating systems considered were two types of Diamond Like Carbon (DLC), a molybdenum coating, nickel-boron, and a nitrided surface. Fretting fatigue tests with specimens coated with DLC had higher fretting fatigue strengths compared to baseline tests and the other coated specimens. The fretting fatigue strength was shown to correlate well with the coefficient of friction between the coated specimen and the bare Ti-6Al-4V pad. In addition to the coatings, two surface treatments, Laser Shock Processing (LSP) and Low Plasticity Burnishing (LPB) were also considered both with and without coatings. Rather than test all five coatings with LSP and LPB, two coatings were selected from the initial five. Results show that the fretting fatigue strength of the samples was markedly increased with or without coatings due to LSP and LPB.