Influence of ammonia on the corrosion behavior of Ti?Al?Zr alloy in 360°C water

The influence of ammonia on the corrosion behavior of Ti−Al−Zr alloy was evaluated in pressurized water at 360°C for 600 days. The results of the corrosion test indicated that the addition of ammonia accelerated the corrosion and hydrogen pickup rates. The oxide scales were composed of a double layer structure, and an inner layer was covered by an outer layer of oxide grains. The XRD studies on the oxide scales showed that the anatase-TiO₂ was continuously transformed into rutile-TiO₂ as the corrosion proceeded. When the same weight gain was considered, the oxide layer grown in water appeared to have a much higher rutile weight fraction than that grown in the ammonia aqueous solution. The deterioration of the corrosion behavior by the ammonia could be mainly attributed to the retardation in the transformation of the oxide structure from a metastable anatase phase to a stable rutile one.