1. Why Hydrogen Control Matters
When the hydrogen content in titanium tubing is too high, impact toughness and notched tensile strength decrease sharply because of hydrogen-induced brittleness. Hydrogen content in titanium tubing is generally specified at no more than 0.015%. To limit hydrogen pickup, remove fingerprints, rolling-mill marks, grease and other residues from parts before heat treatment, and keep the furnace atmosphere free of water vapor.
2. Vacuum Annealing for Hydrogen Removal
If hydrogen content exceeds the allowable value, it must be removed by vacuum annealing - typically at 538-760°C, under a low absolute pressure, holding for 2-4 hours. This drives hydrogen out of the metal while keeping the surface clean.
3. Oxide Film and Oxygen Contamination
Up to about 540°C, the oxide film on the titanium surface does not thicken significantly. At higher heat-treatment temperatures (760°C or above), the oxidation rate accelerates rapidly; oxygen diffuses into the material, forming a diffusion layer (contamination layer) with high brittleness that leads to cracks and surface damage on parts.
4. Removing the Contamination Layer
Mechanical methods: sandblasting, chipping, machining.
Chemical methods: pickling, chemical milling.
During heat treatment: shorten heating time as much as possible while ensuring uniform temperature rise; heat in a vacuum furnace or under inert gas (argon, nitrogen) to avoid or reduce contamination from air-furnace heating.
5. Practical Rules
Clean parts thoroughly before any thermal cycle.
Use vacuum or inert-gas protection for all elevated-temperature processing.
Control temperature and time; never exceed ~760°C without protection.
