Abstract
A number of Al-, Mg- and Ti-base alloys were preconditioned by oxidation via Plasma-electrolytic oxidation (PEO) followed by the addition of Cr and Ni elements in the coating pores by chemical precipitation and a final stage of mechanical treatment. The overall effect was a combination of hardness and resistance to wear. PEO voltage level was found to be a factor decisive for the oxide layer thickness and level of porosity. In turn the latter two factors appeared to act upon the degree of hardening corundum to alumina fraction in the layer and the degree of Cr/Ni penetration into the oxide layer itself. The optimum condition of increased micro-hardness and high resistance to wear was achieved for an AlCu4Mg2 alloy of extended oxide layer thickness and intermediate levels of open porosity. Similarly good wear results were obtained for a Be60AlMg2 alloy of particularly low micro-hardness but of sufficiently high porosity in order to accommodate the Cr/Ni intake.
Highlights
Manufacturing of ceramic-coated non-ferrous alloy components may, in principle, yield benefits over the use of more traditional materials such as ceramics, high-alloy steels and cast iron[1,2]
Based on macroscopic observations during the experiments, plasma conditions were achieved on the sample surface at approximately 140 V AC with the simultaneous release of water vapor generated by the exothermic Plasma-electrolytic oxidation (PEO) reaction
Metallographic examination of the sample crosssections indicated the presence of discharge channels as dark dots distributed unevenly over the coating surface; the frequency of occurrence of the discharge channels appeared to decrease while their diameter increased with increasing AC voltage; these trends are similar to the ones observed for PEO processing of an 6061 alloy[12]
Summary
Manufacturing of ceramic-coated non-ferrous alloy components may, in principle, yield benefits over the use of more traditional materials such as ceramics, high-alloy steels and cast iron[1,2]. Shortcomings of ceramic coatings include poor performance under insufficient lubrication[4], as, e.g. is the case with Ti nitride/carbide coatings[5]; due to the latter’s low wetability, the lubricant film is compromised leading to increased wear. Alternative means of achieving increased wear protection, in the case of Al, Mg and Ti-based alloys, involve the application of various nanofillers in the pores of the ceramic coating; popular such fillers are e.g. fluoropolymers[7] and SiO2 particles applied via sol-gel technology[8]. Such coating augmentation limits applications to low temperatures.
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