Effect of pre-oxidation on the properties of aluminide coating layers formed on Ti alloys

The aluminized and pre-oxidized + aluminized Ti alloys, oxidized at 600 °C in air for 50 h, are studied by SEM and XRD, respectively. The results show that before oxidation the aluminide coating is composed of Al3Ti phase, but the pre-oxidation + aluminide coating consists of Al2TiO5, Al5Ti3 and Al3Ti phases. After oxidation they are both composed of Al2O3 and TiO2. A comparison study has been carried out between two samples to determine the influence of pre-oxidation upon the properties of aluminizing and oxidation resistance. The oxidation kinetics shows that the weight change of pre-oxidized + aluminized sample is less than that of the aluminized sample. The whole thickness of the pre-oxidation + aluminide scale is about half of that of the aluminide scale. The pre-oxidation affects not only the aluminizing but also the adherence between the scale and the substrate. So the pre-oxidation + aluminizing is an effective method to improve the oxidation resistance of Ti alloy.