The corrosion behaviours of Ti60 alloy with solid NaCI in wet oxygen at 600 degree C

摘要

The near-alpha high temperature titanium alloys (like Ti60 alloy) have been considered as a material for compressor blades of aerospace engines, due to their superior strength-weight ratio, good creep resistance against high temperature, and excellent mechanical properties. The service condition of compressor blades is very harsh: middle to high temperature (300-600 degree C), solid salt (especially NaCI) deposit, and water vapour. Generally, the corrosion resistance of Ti alloys is thought to be good. But in fact, we do not know if the corrosion happens or not. Therefore, the corrosion behaviour of Ti60 alloy under solid NaCI deposit in wet O_2 is studied. Ti60 alloy under solid NaCI deposit is subjected to isothermal corrosion in wet oxygen flow at 600 degree C for 100hr. The mass gain results show that NaCI greatly accelerates the corrosion rate of Ti60 alloy, compared to those without NaCI deposit, as shown in Fig 1. The composition and structure information of corrosion products, studied by SEM, XRD and EMPA, indicate that corrosion scale under the synergistic effect of NaCI deposit and wet O_2 is a complex scale with outer and inner layers. The products is loose and with lots of holes, which can work as diffusing paths of corrosion medium and accelerate the corrosion. The results of TEM indicate that Cl ions transport along grain boundaries to corrode the metal and may partial substitutes O in Ti_2O and partly TiO_2. Therefore, the transition of ions in the oxides is significantly increased, which further accelerates the corrosion rate of Ti60 alloy.