Plasma nitride chromium plated coating method

A method of forming a wear-resistant coating for internal combustion engine component parts which allows the part to remain dimensionally stable under severe engine operating conditions is provided. The coating is formed by a two step method. First, the engine part is coated with chromium to form a chromium base layer. Second, the chromium coated part is subjected to a reactive gas plasma in a reaction chamber at an elevated temperature and under an applied electrical potential. The gas of the plasma reacts with the chromium to form the wear-resistant layer. Preferably, the reactive gas is nitrogen which reacts with the chromium to form a chromium nitride surface layer on the chromium base layer. The coating formed in accordance with the present invention is especially suited for fuel injectors because the process may be conducted in essentially two steps so that any resizing of the fuel injector plunger can be done after formation of the chromium base layer, but before the wear-resistant surface layer is formed.