The color changes and tensile properties of oxidized Ti–6A1–2Mo–1.5Cr–2Zr–2Sn–2Nb alloy

Abstract

The oxidation of titanium alloy at elevated temperature severely limits its property and service life. It is a common and urgent issue to assess the mechanical property of oxidized titanium component without destroying its structural integrity. In this work, the color changes and tensile properties of oxidized Ti–6A1–2Mo–1.5Cr–2Zr–2Sn–2Nb alloy with initial basket-weave microstructure were investigated in the temperature range of 100–1000°C. It was found that the oxidized specimens exhibited brilliant and regular color changes. X-ray diffraction (XRD) analysis indicated that the color changes were mainly attributed to the mixing of colored titanium oxides in the oxidation layer (such as yellow TiO, white TiO2 and blue Ti2O3). It was also found that mechanical properties were significant influenced by the oxidation treatment. The specimens oxidized below 600°C exhibited excellent strength and plasticity due to its fine basket-weave microstructure and dense oxidation layer. In the temperature range from 600 to 800°C, the strength slightly decreased while the plasticity rose a little. The change of mechanical properties during the temperature range was mainly determined by the microstructure change. Eventually, both strength and plasticity decreased sharply when the temperature was over 800°C, which was mainly caused by the thick oxidation layer with porous and loose microstructure. The fracture mode of tensile specimens also changed from ductile fracture (below 800°C) to transgranular cleavage fracture (over 800°C). On the basis of experiments, a corresponding relation between the color changes and tensile properties was established. The royal blue should be regard as critical color between the acceptable and unacceptable tensile properties of the oxidized titanium alloy.