Influences of Calcination Ambiences on Morphologies, Phase Composition and Contents of the Elements of Ceramic Coatings on Ti Alloy by Micro-Arc Oxidation

摘要

Compound ceramic coatings with the main crystal phase of Al_2TiO_5 (as-coated samples) were prepared in situ on the surface of Ti-6Al-4V alloy by means of pulsed bi-polar micro-arc oxidation (MAO) in an NaAlO_2 solution. The coated samples were calcined in argon and air at 1000 °C, respectively. The phase composition, surface and section morphology, and element contents of the ceramic coatings were investigated by X-ray diffractometry (XRD), Scanning electron microscopy (SEM) and X-ray fluorescence spectroscopy (XRF). The samples were treated in argon and the as-coated ones were calcined in air at 1000°C to study the anti-oxidation properties of the samples. The results show that Al_2TiO_5 had been decomposed in an hour and transformed into α-Al_2O_3 and rutile TiO_2 in air. However, Al_2TiO_5 had been decomposed in four hours in argon and the final coating surface was completely composed of α-Al_2O_3. The content of Al_2O_3 was decreased from outside to inside layers and Ti_2O_3 was formed in the coating. Furthermore, the morphology of the ceramic coatings after the calcination was different. The coatings calcined in argon were finer; the grains and pores were smaller than those in air.