Effect of heat-treatment processes and high temperature variation of acid-chloride media on the corrosion resistance of B265 (Ti–6Al–4V) titanium alloy in acid-chloride solution

Abstract

Corrosion resistance of untreated (B265TiN), quenched (B265TiQ), and annealed (B265TiA) B265 titanium alloy was studied in 2–10 M H2SO4 + 10% NaCl solution at 30, 70, and 95°C by potentiodynamic polarization, potentiostatic measurement, open circuit potential measurement, and optical microscopy. B265TiN was the most resistant of the alloys to general corrosion at 30°C with values between 0.094 and 3.782 mm/year. B265TiQ exhibited the highest corrosion rate values (0.210–23.399 mm/year). Its plots show significant increase in cathodic slope. At 70 and 95°C, B265TiN exhibited the lowest corrosion rate in 2 and 6 M H2SO4 + 10% NaCl solution, while B265TiQ exhibited the corresponding highest values. Optical characterization shows B265TiN, B265TiQ, and B265TiA alloys are highly resistant to corrosion in 2 M H2SO4 + 10% NaCl at 30°C compared to 10 M H2SO4 + 10% NaCl, where marginal deterioration occurred on B265TiN, significant degradation on B265TiQ, and localized degradation on B265TiA. The extent of degradation increased at 70 and 95°C. B265TiN exhibited the highest resistance to metastable pits formation compared to B265TiQ and B265TiA. Potentiostatic values at 70°C shows high temperature exposure of Ti alloy to accelerated corrosion. Metastable pit initiation values at 70°C are significantly greater. Open circuit potential measurement at 30°C shows B265TiN demonstrated least vulnerability to corrosion with stable oxide formation at 2 M and 6 M H2SO4 + 10% NaCl, and B265TiQ was least vulnerable at 10 M H2SO4 + 10% NaCl. At 70°C, B265TiQ was least vulnerable to corrosion with unstable oxide formation at 2 M and 6 M H2SO4 + 10% NaCl compared to B265TiN at 10 M H2SO4 + 10% NaCl.

Keywords

• titanium
• corrosion
• acid-chloride
• heat-treatment
• pitting
• passivation