Effects of additives on corrosion and wear resistance of micro-arc oxidation coatings on TiAl alloy

Ceramic coating was deposited on TiAl alloy substrate by micro-arc oxidation (MAO) in a silicate-aluminate electrolyte solution with additives including sodium citrate, graphite and sodium tungstate. The microstructures and compositions were analyzed by SEM, EDX and XRD.The corrosion and wear properties of the coatings were investigated by potentiodynamic polarization and ball-on-disc wear test, respectively. The results show that the MAO coatings consist of WO3, Ti2O3, graphite and Al2O3 besides Al2TiO5 and Al2SiO5. With additives in the electrolyte, the working voltage at the micro-arc discharge stage decreases, and the ceramic coating gets smoother and more compact. The corrosion current density of MAO coating is much lower than that of TiAl substrate. It can be reduced from 9.81×10-8 A/cm2 to 3.02×10-10 A/cm2. The MAO coatings composed of hard Al2O3, WO3 and Ti2O3 obviously improve the wear resistance of TiAl alloy. The wear rate is -3.27×10-7 g/(N-m).