The Influence of Temperature on Corrosion Resistance of Ti-Mo Alloy in Acidic Medium

Titanium alloy pipeline is playing an increasingly important role in petrochemical industry. This paper mainly explores the corrosion behavior of Ti-Mo alloy in 20wt.% HCl solution with different temperature changes, aiming at revealing the corrosion mechanism of Ti-Mo alloy and providing certain reference value for the application of Ti-Mo alloy in petrochemical industry. The titanium alloy used in this experiment is produced by CNPC Baoji Petroleum Steel Pipe Co., Ltd. The main components (wt.%) are as follows: 2.99 Mo, 0.60 Zr, 0.044 Fe, 0.014 C, 0.005 1 N, and the balance is Ti. X-ray diffraction (XRD) and Quanta 250 scanning electron microscope (SEM) were used to observe the phase and morphology of Ti-Mo alloy. Electrochemical test adopts typical three-electrode system, with saturated silver chloride electrode as reference electrode, platinum electrode as counter electrode, titanium alloy sample as working electrode with the area of 1 cm2. The electrochemical experiment temperature were 20, 30 50 and 70 °C. The potential range of polarization curve was ‒0.8 V (vs. Ag/AgCl) to 2 V (vs. Ag/AgCl) and the scanning frequency of electrochemical impedance spectroscopy (EIS) was 10−2 Hz to 105 Hz. The chemical composition of the oxide film was studied by 250Xi X-ray photoelectron spectroscopy. The oxide film was formed at 0.5 V (vs. Ref) for 7 200 s. Mott-Schottky was used to explore the properties of semiconductor films. The experimental frequency of Mott-Schottky was 1 000 Hz, the scanning potential was 2 to ‒1 V with the step size of 20 mV. 20wt.% HCl solution was selected as the static immersion test solution, and the temperature of the solution was kept at 20 °C, 30 °C, 50 °C and 70 °C respectively. After soaking for 15 days, ultrasonic cleaning with distilled water and alcohol, drying, weighing with a balance with accuracy of 0.1 mg, and observing the morphology after corrosion with 3D laser confocal and scanning electron microscope. The solution medium temperature produced a great influence on the corrosion behavior of Ti-Mo alloy. The corrosion potential decreased from ‒548.9 mV (vs. Ag/AgCl) to ‒593.3 mV (vs. Ag/AgCl) in the range of 20 to 70 °C. Ti-Mo alloys had the lowest corrosion current density at 20 °C, i. e., 36.925 μA/cm2, and the passive current density decreased as the temperature enhanced. In addition, the content of the oxide film had no obvious difference at various temperature, but the donor concentration in the film increased at elevated temperature. Besides, it caused the n-p type transition of the semiconductor characteristics. The corrosion rate of the Ti-Mo alloy in 20wt.% HCl solution were 1.138 3, 2.931 7, 35.217 and 39.838 6 mm/a when solution temperature were 20, 30, 50 and 70 °C, which indicated that the corrosion rate accelerated with the temperature went by. An increase in the temperature of the solution will promote the formation of defects and reduce the stability and corrosion resistance of the oxide film. The α and β phases form microgalvanic cells in the corrosion process, and the α phase is more prone to corrode acting as the anode, which is due to the higher content of Mo in the β phase. © 2022, Chongqing Wujiu Periodicals Press. All rights reserved.