AVS 51st International Symposium
    Advanced Surface Engineering Monday Sessions
       Session SE-MoM

Invited Paper SE-MoM8
Environmentally Friendly Plasma Electrolytic Processes for Corrosion and Wear Protection of Lightweight Metals

Monday, November 15, 2004, 10:40 am, Room 303D

Session: Nanolayered and Gradient Coatings for Surface Engineering
Presenter: A.L. Yerokhin, Sheffield University, UK
Authors: A.L. Yerokhin, Sheffield University, UK
A. Matthews, Sheffield University, UK
Correspondent: Click to Email
The paper discusses both fundamentals and applied aspects of novel Plasma Electrolytic Oxidation (PEO) processes which can be successfully used for wear and corrosion protection of Al, Ti and Mg alloys. Being a high-voltage electrochemical oxidation process, PEO is featured by a plasma discharge that occurs at the metal/electrolyte interface in the form of discrete short-lived microdischarges moving across the metal surface. This alters the kinetics of the main electrode processes, i.e. anodic oxidation and dissolution, complementing them with high rate gas evolution triggered by plasma enhanced thermochemical reactions at the metal surface. As a result, surface layers with composition and structure substantially different to those of conventional anodic oxide films can be formed in environmentally friendly diluted alkaline solutions. Electrolyte species tend to be more strongly incorporated into the surface layer, forming mixed oxide compounds. Rapid local heating and quenching of the surface during the microdischarge events promotes formation of high temperature oxide phases with fused-like structure, controllable porosity and a graded coating/substrate interface. Oxide ceramic surface layers produced by PEO as well as composite coatings based on these layers are proven to possess excellent tribological and anti-corrosion properties, which show promise for a number of industrial applications.