Fatigue Behavior of Duplex Thermal Spray Coatings on
Steel Substrates for Aircraft Landing Gear Repairs
J. T. Redman, Master’s Candidate, Business
Administration,
* J. W. Presley,* J. R. Shadley, Ph.D.** and E. F. Rybicki, Ph.D.***
Worn aircraft landing gear parts have been repaired for
many years using a filler layer of sulfimate-nickel to restore the parts' original
dimensions followed by a top covering of electroplated chrome to provide a low friction,
wear resistant surface. But, the chromium electroplating process has fallen into disfavor
in recent years due to environmental and economic factors. One of the most promising
alternatives to the sulfimate-nickel-chrome system is a duplex thermal spray coating. A
duplex thermal spray coating consists of a filler layer for dimensional restoration plus a
tungsten carbide top layer for wear resistance. Before duplex coatings can gain acceptance
in the aircraft manufacture and repair industries for replacement of chrome systems, they
must be shown to have comparable wear and fatigue characteristics.
The objective of this research is to
compare the fatigue behavior of several thermal spray duplex systems with the behavior of
the sulfimate-nickel chrome system. Coatings were applied to 0.125? thick test panels of
4340M steel. Coated panels were cycled in flexure. Of primary concern was the initiation
and growth of cracks in the coatings and delaminations between coatings and substrate with
increasing number of cycles. Fluorescent dye penetrant testing was used to observe crack
initiation and growth. Flexure stiffness of each coated test panel was measured
periodically as an indicator of the extent of coating degradation and plotted against the
number of cycles.
This work was supported by the
Oklahoma Center for the Advancement of Science and Technology (OCAST) and Southwest
Aeroservice, Inc., Tulsa, Oklahoma.
* Student Member ASME
** Member ASME
*** Fellow ASME
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