Controlled synthesis of microarc oxidation coating on Ti6Al4V alloy and its antifriction properties

Ceramic coatings were fabricated on a Ti6Al4V alloy surface by microarc oxidation (MAO) in Na₂SiO₃-(NaPO₃)₆ aqueous solutions with and without NaAlO₂ additive using an AC power supply. The effect of NaAlO₂ on microstructure, composition, and homogeneity of ceramic coatings were characterised using SEM, XRD, and EPMA. The antifriction property of the coatings with optimised microstructure sliding against SAE 52 100 steel ball was investigated on a pin-on-disc friction and wear tester. The results show that the addition of NaAlO₂ into Na₂SiO₃-(NaPO₃)₆ solution assists the formation of more dense, uniform, and thicker coatings and increases rutile TiO₂ content in the coatings. The optimised coating sliding against the steel has a friction coefficient as low as 0.2-0.3 at an applied load of 0.5 N and sliding cycle below 2500, which is much smaller than that of uncoated Ti6Al4V against the same counterpart. The transferring of material from the softer steel ball onto the coating surface is the main wear event, while the microarc oxidation coating is characterised by slight abrasive wear and adhesive wear.