PSI - Issue 13

Dan Eliezer et al. / Procedia Structural Integrity 13 (2018) 2233–2238 Eliezer et al/ Structural Integrity Procedia 00 (2018) 000 – 000

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DSS. At this lower dynamic pressure hydrogen has enough time to propagate a crack. This demonstration clearly represents the HAC phenomenon; when hydrogen is presented in a bulk metal it will promote cracking.

(b)

(c)

(a)

Non-charged

DSS SMSS AUSS

H charged

1000

800

600

400

Yield Strength [MPa]

30 MPa H 2 pressure

200

20 μm

20 μm

5 10 15 20 25 30 35 40 45 50 55

Elongation [%]

Fig. 3. (a) Quasi-static tensile test results of gas-phase charged DSS, SMSS and AUSS, and microstructural observations of cross-sectioned dynamic loaded hydrogen charged DSS: (b) non-charged and (c) hydrogen charged.

2.3. The effect of hydrogen-induced second phase on hydrogen trapping mechanism

The hydrogen trapping mechanisms were analyzed using thermal desorption analysis (TDA).The hydrogen evolution rate as a thermally activated process from trap sites were given by Lee and Lee's model [22]: / = ( − ) (− / ), (2) where X is the hydrogen content that escapes a trap, A is the reaction rate constant, E a is the activation energy for releasing hydrogen from its trapping site, R is the gas constant, T c is the peak of the absolute temperature and φ is the heating rate. The trap activation energy is measured from the linear relation [22]: ( / )/ ( / ) = − / , (3) A Peak position is related to a suitable activation energy; higher temperatures indicates higher binding energies, Fig. 4 [2].

Fig. 4. TDS spectra at a 6 o C/min heating rate of 72 h cathodic hydrogen charged samples: SMSS, DSS, and AUSS.

The  -martensite phase trapping site appears only in SMSS and DSS where the  -phase stability is lower and the