Breakthrough Studies on the Plasma Electrolytic Oxidation (PEO) Coating Process

Lead Research Organisation: University of Sheffield
Department Name: Materials Science and Engineering

Abstract

Plasma Electrolytic Oxidation (PEO), also known as Micro Arc Oxidation (MAO), Spark Anodising and Microplasma Oxidation, is a processing technique in which the surfaces of metals such as Al, Mg and Ti are converted into oxide coatings, ranging from tens to hundreds of microns in thickness. Coating growth occurs via large numbers of short-lived sparks (electrical discharges), caused by local dielectric breakdown. The resultant coatings can be highly resistant to wear and corrosion, and adhere exceptionally well to the substrate. Until recently, however, the nature of these plasma discharges, and the links between this and the resultant coating microstructure, have been very poorly understood. Recent work at Sheffield and Cambridge has produced new information about the temperature, density, resistivity, spatial distribution, frequency and duration of these discharges, and also about the influence that these characteristics have on the coating microstructure. The proposed project is aimed at utilising and expanding the techniques that have been developed in this work, employing the researchers primarily responsible for these advances, and also benefitting from the input of experienced plasma physicists based in Southampton. One of the objectives will be to create a new process model. This will give quantitative insights into the interplays between electrical circuitry, electrolyte composition, plasma discharge characteristics and coating microstructure. This should assist in the aim of improving the energy efficiency of the process. The enhanced understanding provided by this modelling will then be utilised to explore the potential for using PEO-like processing to implant small atoms, such as carbon and boron, into metals such as steels, giving increased surface hardness. Preliminary reports of this possibility are encouraging. If it does prove to be viable, then it would offer major energy-saving benefits in competition with conventional carburizing, which requires components to be held at high temperatures for extended periods. The work will be carried out in collaboration with two UK SMEs in the PEO field, and should thus lead to substantial and relatively short term benefits to UK industry.

Publications

10 25 50

 
Description The project has achieved breakthroughs in the fundamental understanding of the plasma electrolysis process, which is becoming increasingly important in many indusrial sectors as a means of enhancing the wear and corrosion resistance of lightweight metals such as aluminium and magnesium. This has been acheived through collaborative experimantal and modelling studies, and will result in improvements in process optimisation and in process diagnostics and on-line control.
Exploitation Route Producers of plasma electrolytic oxidation processes and end-users of the coatings will benefit.
Sectors Aerospace, Defence and Marine,Electronics,Energy,Environment,Manufacturing, including Industrial Biotechology,Transport,Other

 
Description The output of the research is being used by producers of plasma electrolytic coatings and treatments
First Year Of Impact 2011
Sector Aerospace, Defence and Marine,Electronics,Energy,Environment,Healthcare,Manufacturing, including Industrial Biotechology,Transport
Impact Types Societal,Economic

 
Title High speed synchronised electrical/optical monitoring of the PEO process, using parallel small area samples 
Description The electrical discharges that take place during PEO are central to understanding and control of the process. It's now known that they have a very short lifetime (~tens or hundreds of microseconds), but tend to occur in "cascades" that persist in the same location for hundreds or thousands of discharges, with a relatively short "incubation period" between each one (that probably corresponds to the period required for the large void left at the site concerned after collapse of the plasma to refill with electrolyte). This understanding has largely arisen from the technique developed in the Gordon Lab. for synchronised monitoring of the electrical current through, and the light emission from, a small area sample (~1 mm diameter) connected in parallel with the main sample. At any given time, there will be no more than one discharge occurring on the small sample, so the associated characteristics can be monitored. 
Type Of Material Improvements to research infrastructure 
Year Produced 2015 
Provided To Others? Yes  
Impact This technology has led to detailed study of various characteristics of the PEO process, including the incidence of cathodic discharges, the "soft regime" etc. 
URL http://www.ccg.msm.cam.ac.uk/research-areas/the-plasma-electrolytic-oxidation-peo-process
 
Description Link with industrial company 
Organisation Cambridge Nanolitic Ltd
Country United Kingdom 
Sector Private 
PI Contribution Provision of research support
Collaborator Contribution Provision of facilities and materials.
Impact New processes and products
Start Year 2006
 
Description Link with industrial company 
Organisation Cutting and Wear
Country United Kingdom 
Sector Private 
PI Contribution Provision of research support
Collaborator Contribution Provision of facilities and materials.
Impact New processes and products
Start Year 2006
 
Description Link with industrial company 
Organisation Keronite International
Country United Kingdom 
Sector Private 
PI Contribution Provision of research support
Collaborator Contribution Provision of facilities and materials.
Impact New processes and products
Start Year 2006
 
Description Link with industrial company 
Organisation Plasma Coatings Group
Country United Kingdom 
Sector Private 
PI Contribution Provision of research support
Collaborator Contribution Provision of facilities and materials.
Impact New processes and products
Start Year 2006
 
Description Link with industrial company 
Organisation Wallwork-Cambridge/Tecvac Ltd
Country United Kingdom 
Sector Private 
PI Contribution Provision of research support
Collaborator Contribution Provision of facilities and materials.
Impact New processes and products
Start Year 2006