Microstructure and morphology of surface oxide films on Ti–6A1–4V

The microstructure of anodic oxide films grown on Ti–6A1–4V in H₂SO₄ was investigated by SEM, TEM, STEM, EDX, and AES, as a complement to a recent surface spectroscopic investigation of the same oxides by XPS, AES, and SIMS. The anodic oxide films are heterogeneous and the texture reflects the duplex microstructure (α and β phases) of the underlying metal. Porous oxide regions are observed with different appearances on α-phase and mixed-phase regions. The oxide films are essentially amorphous in the investigated thickness range 60–300 nm (in contrast to as-grown anodic films on pure Ti), but crystallize to the anatase structure upon annealing. Considerable lateral variation of the V content in the oxide is observed, reflecting the corresponding variation in the underlying metal. The results are compared with a previous, similar investigation of anodic oxides on pure Ti.