Method for coating joint surfaces of metals used to form prostheses

A process electroplates a metal workpiece with thin dense chromium. The workpiece is first activated by submerging in an aqueous solution of sulfuric acid and a biflouride salt, preferably ammonium biflouride. The biflouride salt reacts to form HF. A preferred activating bath has a 35% sulfuric acid concentration of 4 ounces per gallon of ammonium biflouride salts. A positive DC voltage is applied between the workpiece and a cathode in the bath. The workpiece is then submerged in a chromium plating bath formed of chromic acid sulfate to produce the chromium plate. A DC plating voltage initially 3 volts produces a current flow of about 1.5-2.5 amps per square inch of workpiece area. In a preferred process, the plating voltage is continuously increased to an eventual value of about 4.5 v. The process is particularly suited to plating cobalt-chromium alloys.