20

40 60 80 100 120 140 corrosion time, h (b)

FIGURE 9.26 Total hydrogen content of corroded specimen as function of exposure time to exfoliation solution (a-d) corresponds to trapping states T1-T4, respectively.

The critical temperature of 500° C, which marks hydrogen evolution from state T4, coincides with the dissolution temperature of the Al2Cu precipitate, as calculated by the computational alloy thermodynamics software ThermoCalc [77]. Thus, trapping state T4 should be associated with this phase. Indeed, it has been demonstrated by tritium autoradiography [47] that the bulk of the 0 precipitate can serve as a hydrogen trap.

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