Multilayer protective coating and method

DETAILED DESCRIPTION Referring to the figures generally and in particular to FIG.
1, there is illustrated greatly enlarged in sectional view a protective coating 10 in accordance with the invention that has been applied to a substrate 12.
As previously described, for wear applications, it is desirable that the substrate have microscopic surface relief or microscopic deviations from a planar surface.
This allows a plurality of the layers of protective coating 10 to be exposed during use, allowing the exposed surface to exhibit the properties of the materials present in the individual layers.
Substrate 12 is illustrated in perspective view in FIG.
2 prior to application of protective coating 10.
The surface 14 of substrate 12 to which protective coating 10 is applied is macroscopically planar but microscopically nonplanar having microscopic surface relief.
In this case, the surface relief consists of a plurality of peaks 16.
Peaks 16 are microscopic surface imperfections or defects which may or may not be essentially randomly oriented on surface 14.
Peaks 16 are illustrative of one type of microscopic surface relief imperfection which may be encountered.
Another type of microscopic surface imperfection consists of "ridges", shown and hereinafter described with respect to FIGS.
5-7.
Other microscopic surface imperfections may consist of, for example, combinations of peaks and ridges, or any type of variation from a planar surface.
Virtually every surface that will be encountered will have such microscopic deviations from a planar surface.
Protective coating 10 may be a wear resistant coating which is made up of a plurality of repeating overlaying multilayer units 18.
Each multilayer unit is made up of two compositionally different layers indicated in FIG.
1 by reference letters "a" and "b".
One or both layers of multilayer unit 18 may be chosen for hardness or wear resistance, or one layer may be chosen for hardness or wear resistance (aluminum oxide, for example) and the other layer chosen for lubricity (molybdenum diboride, for example)