Surface treatment of titanium and 4340 steel for electroplating

Treating titanium substrates with a hot mixture of formic acid and sodium dodecyl sulfate (SDS) has been found to improve the adhesion of a plated chromium coating. Treating 4340 steel substrates with a hot mixture of formic acid and SDS has been found to increase the thickness of a plated chromium coating. The goal of this work was to determine the changes that formic acid and SDS make on 4340 steel and titanium surfaces. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to examine the metal surfaces before and after formic acid and SDS treatment. Treatment of 4340 steel with a mixture of formic acid and SDS was found to etch the steel surface and increase the nickel surface concentration. The increased nickel surface concentration may be the reason for a thicker chromium coating after the treatment. Treating titanium with a mixture of formic acid and SDS did not change the morphology of the titanium surface. However, a small metallic titanium peak and titanium suboxide peak were detected in the Ti 2p XPS spectrum of the treated sample. These changes in the titanium oxide layer on the titanium surface are thought to be responsible for improvement in the adhesion of the chromium coating.