Some Effects of Microstructure and Chemistry on Corrosion and Hydrogen Embrittlement of Ticode–12

Abstract

ABSTRACTEffects 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).