Surface Characteristics and Tribological Performance of Plasma Electrolytic Oxidation (PEO)-based Coating Systems on Al and Ti Alloys

Abstract

High friction can introduce the generation of localised heat, severe surface degradation and material losses at the contact area of metallic workpieces. An effective method to improve the wear resistance of lightweight metals is to coat the alloys with a thick and hard oxide coating, and the PEO technique was reported to effectively fulfil that requirement. This research optimised the electrolytic parameters to produce thick and hard PEO coatings on Al and Ti alloys and investigated the tribological performance of different combinations of liquid/solid lubricants on PEO coatings under fretting regimes and reciprocating wear. A duplex coating, comprised of graphite/MoS2/Sb2O3 layer deposited on top of a PEO treated 6082 series Al alloy substrate was subjected to a series of fretting wear tests. The resultant duplex coating was demonstrated to efficiently enhance the wear performance of the Al alloy. Specific stick-slip (~3 micrometre amplitude), partial slip (5-10 micrometre) and gross slip (>10 micrometre) regimes were observed, with about an order of magnitude improvement over a single layer PEO coating. The high initial contact pressures (~1.1 GPa) with a bearing steel counterpart under oxidising atmosphere increased friction due to generation of Fe/Al/Cr oxides/hydroxides in the contact region, leading micro-cracking in the PEO coating followed by fatigue damage of the Al substrate. Reducing contact pressure to

Date of Award	31 Dec 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Ping Xiao (Supervisor) & Allan Matthews (Supervisor)