Spray shadowing for stress relief and mechanical locking in thick protective coatings
A method for applying a protective coating on an article, comprising the following steps: selecting an article with a surface for applying a coating thickness; creating undercut grooves on the article, where the grooves depend beneath the surface to a bottom portion with the grooves having an upper width on the surface and a lower width on the bottom portion connected by side walls, where at least one of the side walls connects the upper width and the lower width to form an undercut angle with the surface less than 90°; and, applying the protective coating onto the article to fill the undercut grooves and cover the surface, thereby forming weak paths within the protective coating.
1. A method for applying a protective coating on an article, comprising the following steps in the order named:
(a) selecting an article with a surface for applying a coating thickness of said protective coating,
(b) creating undercut grooves on said article, where said grooves depend beneath said surface to a bottom portion, said grooves having an upper width on said surface and a lower width on said bottom portion connected by side walls, where at least one of said side walls connects said upper width and said lower width to form an undercut angle between said side wall and said surface that is less than 90°, and
(c) applying said protective coating onto said article by a technique selected from vapor deposition, thermal spraying, or atomized liquid spray so that said protective coating fills said undercut grooves and covers said surface thereby forming weak paths for stress relief within said protective coating.
2. The method of claim 1 wherein said coating thickness is measured from above said surface, and where said undercut grooves are created with a depth measured from below said surface, and corresponding to a range from about 0.1-1 times said coating thickness, said lower width having a range of about 0.1-100 times said depth, said upper width having a range of about 0.1-100 times said depth, and said undercut angle having a range from about 30 degrees to less than 90 degrees.
3. The method of claim 1 further including sintering of said article to strengthen said protective coating.