S. Clouser, D. Radatz, SIFCO Applied Surface Concepts, Independence, OH; A. Zhecheva, SIFCO Applied Surface Concepts, Bromsgrove, United Kingdom
The application of a coating to the surface of titanium can improve tribological properties and increase titanium’s usefulness in aerospace applications. The inherent difficulty caused by the oxide film with plating a coating onto titanium alloys was overcome by the use of a selective electroplating process. The surface of titanium 6Al-4V was subjected to electrochemical treatments to increase surface area, remove the oxide film, and immediately apply an adherent metallic coating by brush plating. The anodic pretreatment microroughened the surface while the cathodic pretreatment reduced the oxide. A nickel strike electrolyte applied directly into the anode – cathode gap to displaced the pretreatment solution while the titanium surface was maintained under cathodic potential control to prevent titanium oxides from reforming. The thin nickel strike layer was used as the substrate to buildup duplex coatings. The adhesion of the coatings to titanium 6Al-4V was verified by passing bend, chisel, heat-quench, scribe, and tape tests. The non-hydrogen embrittlement nature of the process was demonstrated by static loading at 85% yield strength without fracture. The coatings can improve the wear, galling, conductivity, and lubricity of the Ti 6-4 surface and are useful in brazing, resizing and repair applications.
Summary: A selective plating process was demonstrated to produce adherent coatings on titanium alloys. The process sequentially anodically microetchs the titanium alloy surface to increase surface area, cathodically reduces the oxide film to expose titanium metal, and electrodeposits a nickel strike layer on and into the microroughened titanium metal surface. The thin nickel strike layer is used as the substrate to build up duplex coatings. The adhesion of the coatings to titanium 6Al-4V was verified by passing bend, chisel, heat-quench, scribe, and tape tests. The non-hydrogen embrittlement nature of the process was demonstrated by static loading at 85% yield strength without fracture. The coatings can improve the wear, galling, conductivity, and lubricity of the Ti 6-4 surface and are useful in brazing, resizing and repair applications.
