ELECTROCHEMICAL BEHAVIOUR OF THERMALLY TREATED Ti-1Ni-0.5Mo ALLOY IN SULPHURIC ACID SOLUTIONS

ABSTRACT

The influence of the metallurgical treatment (by forging) and of the plastic deformation degree (four different degrees) on the electrochemical behavior of the ternary alloy Ti-1Ni-0.5Mo in sulfuric acid solutions of different concentrations (5% and 30%) and temperatures (25^○, 50^○, 75^○C) in comparison with the base metal is studied in this paper. The alloy corrosion potentials are nobler than that of titanium due to the favorable effect of the alloying elements. The passive potential range of the casting and forging alloy is lower than that of the titanium. This behavior is due to the alloying elements, which are in the transpassive dissolution state in this potential range. The casting alloy has a reduced stability of its surface state, both by the higher values of the anodic dissolution current densities in the passive state and by the transpassive potential, which is lower than the forging alloy. The metallurgical working by forging improves the passive film stability, enlarging the passive potential range and decreasing the dissolution current density in the passive state. This fact is confirmed by the corrosion rates, which show that the forging alloy is more resistant than the casting alloy. The plastic deformation degree ϵ (ϵ = 29.7%, 45.74%, 62%, and 85.8%) influences the corrosion critical current densities and the corrosion rates; the two parameters decrease with an increase in the plastic deformation degree.

Key Words:

• Acid solutions
• Casting and forging Ti-1Ni-0.5Mo alloy
• Corrosion resistance
• Electrochemical parameters
• Linear polarization
• Plastic deformation
• Potentiodynamic polarization
• Potentiostatic polarization
• Thermal treatments

ACKNOWLEDGMENT

The authors gratefully acknowledge support by the Romanian Academy Program.

Notes

^aTi-1 Ni-0.5 Mo_f was not deformed before corrosion.