Published online by Cambridge University Press: 21 February 2011
Effects of microstructure and chemistry on corrosion and hydrogen embrittlement of TiCode-12 have been investigated. Heat treating mill-annealed TiCode-12 in the temperature range 500–750°C results in a sensitization effect, i.e., an increase in the uniform corrosion rate when tested in either boiling 1N HCl or a MgCl2 brine. This effect is caused by microstructural changes involving the precipitation of Ti2Ni. Electrochemical studies indicate that sensitization results from galvanic coupling between Ti2Ni, acting as cathode, and the α-Ti matrix with resultant shifts in corrosion potential. Increasing the Fe content of the alloy promotes the sensitization effect.
Hydrogen embrittlement of TiCode-12 was studied using the slow strain rate technique. Hydrogen concentrations to 130 wppm did not cause embrittlement. However, above 220 wppm hydrogen, degradation was observed as a decrease in mechanical behavior and the appearance of cleavage-like secondary cracks. The embrittlement was dependent on temperature and alloy chemistry but not environment (air or brine).
This work performed at Sandia National Laboratories supported by the U.S. Department of Energy under contract number DE-AC04–76DP00789.