Microstructural Characterization of Multi Layered Plasma and HVOF Coatings

In this work, variable compositional Plasma and HVOF coating layers (multi layered) of eight different coating techniques were examined and exposed to corrosive/erosive environments to assess the microstructural characterization as well as the mechanical properties of the applied coatings. Different coating systems were applied on a base metal. The work includes application of coating layer of tungsten carbid-cobalt and application of various three layer combinations of coating on the same base metal at different percentages keeping the thermal spray parameters and the coating thickness constants. Transition coating (graded) using plasma spray with multiple feeders was also investigated and compared to the outcome results of the HVOF coating.  The surface morphology and the elemental composition of the coatings before and after each test were examined using SEM and EDS techniques. 

 The produced coating materials were also subjected to several mechanical and chemical tests - including bending, fatigue, erosion-corrosion, and tensile testing to determine the effect of possible failures when subjected to sever corrosive and erosive environments.
Results indicated that multilayer coating increases the material performance when subjected to both corrosion and erosion environment.  There was no effect on having different layers comparison on both coating porosity and oxides and thereby their mechanical properties compared to the one layer coating.  Multilayer coatings had a better performance in aggressive corrosive environment when compared to conventional single layer coating.