Abstract
Micro-arc Oxidation (MAO) process is a plasma assisted electrochemical process, which allows formation of ceramic-like dry oxides on top of light alloys surfaces. The good corrosion resistance as well as the low density of titanium alloys are recognized and so required for conception of structural parts in marine environment. However, their tribological behaviour reveals an important tendency to stick-slip phenomenon, which makes use of these alloys for dynamic contact mechanisms difficult. Through the MAO project from IRT M2P, formation of a MAO coating composed of aluminium titanate has been investigated to improve tribological behaviour of a commercially pure titanium (Grade 2) and an α+β alloy (TA6V, Grade 5). Pin-on-disc testing has been carried out to evaluate friction coefficient and the presence or not of stick-slip phenomenon in various contact configurations (involving non-treated titanium surfaces, MAO treated surfaces, with steel or titanium balls …) in dry or artificial seawater media. Those test campaigns are completed by evaluation of fatigue behaviour, and tribological testing on a demonstrator. Finally, this study highlights influence of MAO coating on diminishing (to removed) stick-slip phenomenon, accompanied by a reduction of friction coefficient, whatever the kind of contact (single treated surface or both ones) and the medium.
Highlights
Titanium alloys are employed for many various applications, due to their low density and their very good corrosion resistance
Micro-arc oxidation (MAO) coatings obtained at 30 A.dm-2 provide a rougher surface and a thicker oxide layer than those obtained at lower current density (10 A.dm-2)
Linear ball-on-disk test results on Grade 2 titanium substrate with and without MAO coating For large ball-on-disk displacements under dry conditions, measured friction coefficients obtained after 5000 cycles present a decrease of 50 % for the contact “Grade 2 – Grade 2 with MAO” compared to the contact “Grade 2 – Grade 2” without any MAO coating
Summary
Titanium alloys are employed for many various applications, due to their low density and their very good corrosion resistance. Micro-arc oxidation (MAO) or plasma electrolytic oxidation (PEO) is an anodizing process, mainly applied to light metals and valve metals such as aluminium, titanium and magnesium This process involving high voltage favours the growth of a thick ceramic-like oxide and allows the formation of multi-functional coatings [1,2,3]. Such a coating is studied here to prevent seizing and to improve tribological performance of titanium alloys by friction coefficient reduction. Adherence and roughness are both determining factors for wear resistance and tribological behaviour of MAO coatings. The main purpose of this study is to test a selection of MAO coatings under various friction conditions, to evaluate impact of test procedures and coating characteristics on the coating friction behaviour and wear resistance
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