Effect Of Na2wo4 In Electrolyte On Microstructure And Tribological Behavior Of Micro-Arc Oxidation Coatings On Ti2alnb Alloy

Micro-arc oxidation (MAO) ceramic coatings were prepared on Ti2AlNb alloy in silicate/ phosphate electrolytes with different concentrations of Na2WO4. The influence of Na2WO4 on the coating growth process, coating structure and composition was analyzed by SEM, XRD and XPS. The tribological behavior of MAO coatings was evaluated by the ball-disc wear test. The results show that the growth rate of MAO coating in electrolyte without Na2WO4 is only 0. 08 mu m/min, meanwhile, the coating is loose and rough, and "networks" connecting with big pores exist on the coating surface. The main phase compositions of this coating are rutile TiO2, anatase TiO2, Al2O3, and Nb2O5. The addition of Na2WO4 in the electrolyte shortens the time before sparking of Ti2AlNb alloy, increases the growth rate of the coating, improves the uniformity of coating and meanwhile, a small amount of WO3 is introduced in the coating. Besides, MAO coatings formed in the participation of Na2WO4 have better wear resistance. Severe abrasive wear occurs when the test is made on Ti2AlNb alloy with Si3N4 the friction coefficient reaches 0. 5-0. 7. Both the friction coefficient and wear rate decrease obviously when Ti2AlNb is treated by MAO. The friction coefficient and wear rate of MAO coating prepared in the electrolyte with 4g/L Na2WO4 are 0. 24 and 6. 2 X 10(-4) mm(3) (N . m) , respectively. Only "fish scales" caused by fatigue wear appears on the coating surface.