The Effect of Off-Angle Spraying on the Structure and Properties of HVOF WC/CoCr Coatings

摘要

The aerospace industry currently applies high velocity oxy-fuel (HVOF) coatings to turbine engine, structural, and landing gear components. An increasing demand for HVOF wear resistant coatings to replace electrolytic hard chrome (EHC) on landing gear components has renewed focus on the spray limitations of HVOF WC/CoCr. One such limitation resulting from the line-of-sight HVOF process is the spray angle. In this study, HVOF WC/CoCr coatings were sprayed at several angles while maintaining consistent combustion characterisitcs and standoff distance. The measured responses included tensile bond strength, microhardness, residual stress, coating surface roughness, and dry fretting wear resistance. Fatigue response was also of interest, but no results were available at the time this paper was written. The microstructure of each coating was examined, both normal to the surface and in cross section. Coatings sprayed at 90° exhibited the highest microhardness and most compressive residual stress, both considered favorable for good wear response. But these coatings also exhibited the highest as-sprayed roughness, least homogeneous microstructure normal to the surface, and lower wear resistence compared to the off-angle coatings; however, the off-angle coatings apear to cause greater wear of the contacting surface. The microstructural differences among the coatings are related to the measured responses.