Effect of Sc(NO₃)₃ on the characteristics of micro-arc oxidation coating formed on TC4 alloy

Abstract To study the effect of Sc(NO 3 ) 3 on the micro-arc oxidation (MAO) coating formed on TC4 titanium alloy, different concentrations of Sc(NO 3 ) 3 were added to the basic electrolyte to prepare the coating. The surface morphology, phase composition, wear resistance, and corrosion resistance of the coatings were characterized, utilizing SEM, EDS, XRD, XPS, a multifunctional material surface tester, and an electrochemical workstation. The results demonstrated that the appropriate addition could raise the oxidation voltage and modify the coating surface morphology and structure. The main phases of the coating were rutile TiO 2 , anatase TiO 2 , SiO 2 , and Sc 2 O 3 . At a concentration of 1.2 g·l −1 , the thickness and hardness of the coating reached the maximum values of 37.07 μm and 457.76 HV, respectively. The roughness and friction coefficient reached the minimum values of 3.648 μm and 0.3328, and the volume wear rate decreased to 0.0131 mm 3 ·m −1 ·N −1 . The corrosion current density and corrosion rate declined to the minimum values of 7.0753 × 10 −9 A·cm −2 and 3.2380 × 10 −3 mpy, respectively, which were improved by two orders of magnitude compared to that of the substrate (5.7335 × 10 −7 A·cm −2 and 2.6239 × 10 −1 mpy). The wear and corrosion resistance of the substrate titanium alloy was enhanced significantly after MAO treatment.