Preparation and high temperature tribological properties of microarc oxidation ceramic coatings formed on Ti2AlNb alloy

Abstract

This present work concentrates on the influence of microarc oxidation ceramic coatings on microstructure and tribological properties of Ti2AlNb alloy. A variety of ceramic coatings are formed on Ti2AlNb alloy in NaAlO2 and Na2SiO3 electrolytes, respectively. A two-step voltage-controlled technology was also used to tailor the microstructure of MAO coatings by adjusting the oxidation time. Microstructure was investigated by using a glancing incidence X-ray diffractometer, a scanning electron microscope, an eddy current thickness meter and a contact surface profiler. The adhesive strength of ceramic coatings to the substrate was tested by a direct pull-off method, and reaches up to 35±3MPa for the two-step voltage-controlled ceramic coatings. Tribological properties of coatings were tested by using a ball-on-disk high temperature friction and wear tester in dry sliding against sintered Si3N4 ball at both room temperature and 600°C. Tribological properties of ceramic coatings are distinctly better than those of Ti2AlNb alloy at both room temperature and 600°C. The dominated wear mechanisms of ceramic coatings are mechanical polishing and brittle microfracturing at room temperature, however, fatigue wear and adhesive wear are also responsible for the material removal at 600oC. The ceramic coatings prepared in the NaAlO2 electrolyte by a two-step voltage-controlled technology have a relatively high wear resistance, and their wear rates are 8.28×10–6mm3N–1m–1 at room temperature and 6.07×10–6mm3N–1m–1 at 600°C. However, the ceramic coatings doped with SiC prepared in the Na2SiO3 electrolyte exhibit low friction coefficients in dry sliding against Si3N4 ball, and their average friction coefficients are 0.45±0.03 at room temperature and 0.55±0.05 at 600°C.