Failures of Thermal Spray Coatings

Many arc sprayed, plasma and even HVOF coatings actually fail rather than wearing out.  The main cause of these failures is the porosity in the coating.  Corrosive vapors, gases, or fluids work their way thru the porosity and cause the parent material's interface to react and delaminate the coating.  These micro cracks start and continue until larger segments come off the part and cause a major failure like a shaft seizure to bearing destruction.  Now you are saying I know that and I use a bond coat and paint the coated surface.  Therefore it will not fail, unfortunately you are wrong.  This paper is to point out why these failures are over looked and do not need to happen if the proper application is done.