Which media cause SCC for commercial titanium alloys?

• A. Hot salt above 275 C
• B. 10% Hydrochloric acid slightly above room temperature
• C. Nitrogen tetroxide or red fuming nitric acid
• D. All of the above

Answer: (D)

The key idea is that titanium alloys can suffer stress corrosion cracking when a tensile stress is present in media that destabilize their protective oxide film. Each environment listed undermines that film or creates conditions that promote localized dissolution or hydrogen embrittlement, enabling crack initiation and propagation under load.

Hot salt above 275 C presents a high‑temperature chloride environment. Chloride ions aggressively attack the passive TiO2 film, promoting pitting and localized dissolution at crack tips and along grain boundaries, which can drive SCC under sustained stress.

A 10% hydrochloric acid solution, even slightly above room temperature, also challenges the protective oxide with chloride ions. Under stress, this can lead to film breakdown and localized corrosion at crack tips, facilitating crack growth.

Nitrogen tetroxide or red fuming nitric acid are strong oxidizing media. Their oxidizers overwhelm the passive film, create highly aggressive conditions at the metal surface, and promote cracking under tensile stress through accelerated anodic processes and hydrogen-related mechanisms.

Because each of these environments can induce SCC in commercial titanium alloys when the right combination of temperature, chloride content, oxidizing potential, and applied stress exists, all of the above media are capable of causing SCC.