Characterization of microporous oxide layer synthesized on Ti-6Al-7Nb alloy by micro-arc oxidation.

In this work a microporous oxide layer was formed on two phase (a+β) Ti-6Al-7Nb titanium alloy by the micro-arc oxidation process in an electrolyte containing (CH3COO)2CaH2O and Na3PO4. The thickness of the surface layer was in the range of 2.7 µm-3.6 µm. Microstructure of the surface layer and the substrate alloy was characterized with use of scanning- and transmission electron microscopy as well as by X-ray diffractometry. The microstructure of the surface layer consisted of TiO2 rutile and anatase nanocrystals as well as of amorphous regions containing mainly Ti, Ca and O atoms and a minority of P, Al and Nb ones. The surface layer was highly porous. The open pores, with diameter up to 6 µm, were homogenously distributed in the specimen surface. Electron tomography was used to investigate the pores morphology and spatial distribution. It was found that open pores exhibited a complex geometry. The closed pores had nearly spherical shape. Adhesion of the surface layer to the titanium alloy substrate was investigated by means of the scratch-test. The value of critical load LC2=14 N indicates a good layer adhesion to the underlying substrate. [ABSTRACT FROM AUTHOR]