High density and adhesion coating process and coatings formed thereby

Abstract

A process of applying a coating to a substrate is provided. A layer of a metallic or ceramic material is applied on the substrate by a thermal spray process. The layer is then subject to plasma electrolytic oxidation (PEO) processing to densify the layer such that a porosity of the layer after PEO processing is lower than a porosity of the layer before PEO processing, or modify the layer by incorporating additional ceramic phases from the electrolyte bath into the densified layer, or improve the adhesion of the thermal spray layer. A base layer may be applied to the substrate with PEO processing before the above referenced layer is applied and/or a ceramic topcoat may be applied to the above referenced layer by a thermal spray process.

We claim: 
     
         1 . A coating on a substrate, comprising a layer initially produced by a thermal spray process and thereafter modified or densified by a plasma electrolytic oxidation (PEO) process, wherein the layer is an oxide ceramic composite layer with a porosity of less than 4%, an oxide content of 60 to 100 vol. %, a hardness of HV0.3 600-1800, and a surface roughness Ra of less than 2 microns. 
     
     
         2 . The coating according to  claim 1 , further comprising a base layer formed by PEO processing on which the layer produced by the thermal spray process and thereafter modified or densified by the PEO process is formed. 
     
     
         3 . The coating according to  claim 1 , further comprising a ceramic topcoat formed by a thermal spray process on the layer produced by the thermal spray process and thereafter modified or densified by the PEO process. 
     
     
         4 . The coating according to  claim 1 , wherein the layer comprises a compound including at least one of aluminum, magnesium, titanium, yttrium, zinc, zirconium, niobium, cerium, and tantalum. 
     
     
         5 . The coating according  claim 1 , wherein the layer has a thickness of 5 to 100 μm. 
     
     
         6 . A method of making the coating according  claim 1 , wherein, during PEO processing, a bipolar waveform with an anodic voltage in the range 400-700V and a cathodic voltage in the range 50-300V is used. 
     
     
         7 . A process of applying a coating to a substrate of electrical conductor, comprising the steps of:
 forming a first layer of ceramic material on a metallic substrate by a plasma electrolytic oxidation (PEO) process; and   forming a second layer on the first layer by a thermal spray process;   wherein, during the PEO process, a bipolar waveform with an anodic voltage in the range 400-700V and a cathodic voltage in the range 50-300V is used.