Electrolytic Plasma Processing for Sequential Cleaning and Coating Deposition for Cadmium Plating Replacement
Abstract
The technique of Electro-Plasma Processing (EPP) was developed and evaluated for DoD use. The EPP process is a high voltage aqueous process (150-200V) that takes place in an electrolyte jet or foam. It can be used to clean metal surfaces or to deposit alloy coatings, the easiest and most common of which are Zn-based. The process operates in the continuous discharge region of the electrolytic current-voltage curve, where the cathodic workpiece is covered with a plasma envelope from a layer of hydrogen electrolyzed at its surface. Material from the solution is deposited by a combination of electrolytic deposition and evaporation across the hydrogen layer. When used as a cleaning method, the technique produces a very clean, roughened, practically amorphous surface comprising a thin heat-treated outmost layer (0.5-2m or 0.00002-0.0001" thick). Nevertheless, there was no measurable fatigue debit for EPP-cleaned surfaces. Nor was there any hydrogen embrittlement, even though copious quantities of hydrogen are evolved in the process. When used as a coating method, the technique produced nodular coatings with very high porosity. A number of different coating chemistries were evaluated, culminating in corrosion, embrittlement and fatigue testing of ZnNi with chromate (Dipsol IZ-258S) and trivalent chrome (Metalast TCPHF) sealers, and ZnMg with a phosphate/silicate sealer. Again there was no hydrogen embrittlement, but there was a fatigue debit of perhaps a factor of two, with a larger debit for ZnNi at high stress (above 130ksi). This debit is similar to that caused by standard electroplated alkaline ZnNi.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 2008
- Accession Number
- ADA520700
Entities
People
- Keith Legg