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The susceptibility to environment-assisted cracking (EAC) of super-elastic TiNi alloy was investigated as a function of the electrochemical potential and solution pH. The investigation was conducted using a slow-strain-rate tensile test apparatus with a potentiostat. The test solutions were sulfate solutions with various pH values adjusted by H 2 SO 4 or NaOH. The alloy deforming under cathodic reaction fractured under the relatively small strain where the alloy was in the stress-induced martensitic phase. A larger EAC susceptibility was obtained at lower potential and lower pH, which indicates that this is a general feature of hydrogen embrittlement. The severe EAC region of TiNi alloy was different from that of TiAl alloy. The EAC susceptibility was strongly correlated with the cathodic charge density, irrespective of the pH or potential: a charge density below 0.025 MC m −2 yielded almost no EAC; however, above 0.025 MC m −2 EAC was induced, and the EAC susceptibility was independent of the charge density. Hydrogen in solid-solution state was detected in the alloy at a charge density below 0.025 MC m .

We have investigated influence of concentrations of LiOH and Li 2 MoO 4 on corrosion behavior of SS400 carbon steel immersed in concentrated LiBr solutions at 393 and 438 K for a short period about 0.2 ks. The corrosion behavior was evaluated by measurement of polarization curve. As a result, the following were obtained: Addition of LiOH to 65 mass% LiBr solution induced suppression of cathodic current around the corrosion potential to shift the corrosion potential lower. Further, two-step active dissolution current was found around the corrosion potential and passive current in the higher potential region. On the other hand, addition of 0.03 mass% Li 2 MoO 4 to 65 mass% LiBr + 0.2 mass% LiOH solution induced small suppression of cathodic current around corrosion potential, and more addition of 0.06 mass% made the cathodic current slightly increase. Two-step active dissolution and passivation phenomena were found in the anodic polarization curve like those in the solution without Li 2 MoO 4 . The anodic current density was almost independent of the concentration of Li 2 MoO 4 . Corrosion rates of the steel immersed in various solutions at 393 K for the short period were almost the same as 1.5 A m 2 . In the solutions at 438 K, corrosion rate decreased with an increase in LiOH concentration and increased with an increase in Li 2 MoO 4 concentration.

The behavior of environment-assisted cracking (EAC) for super-elastic TiNi alloy was investigated as functions of solution pH and electrochemical potential. The specimen was immersed in sulfate solutions at various pHs, and subjected to a potentiostatic slow strain rate tensile test. As a result, the EAC map for the TiNi alloy as functions of the solution pH and the applied potential was successfully produced, and it was revealed that larger EAC susceptibility was obtained in the region of lower potential and lower pH. The tendency was quite typical for hydrogen embrittlement, but not similar to that of TiAl. The EAC susceptibility was classified by cathodic charge density, irrespective to pH nor potential: The charge density larger than 0.025 MC.m-2 induced a maximum EAC susceptibility.

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