PSI - Issue 54

Lisa Claeys et al. / Procedia Structural Integrity 54 (2024) 250–255 Claeys/ Structural Integrity Procedia 00 (2023) 000 – 000

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and (Zhao, et al., 2018) have observed less severe embrittlement, however, their hydrogen concentration were also far less than the ones obtained with the charging conditions in this work.

0.30

(a)

(b)

5.0

0.25

4.0

0.20

3.0

0.15

2.0

0.10

HEA 900 K/h 304L 900 K/h

HEA ISO_500 HEA ISO_400 HEA ISO_300

1.0

0.05 Hydrogen [wppm/s]

HEA 900 K/h FIT 304L 900 K/h FIT

Hydrogen [wppm/s]

0.0

0.00

0

200 400 600 800 1000

0 100 200 300 400 500 600 700 800

Temperature [ C]

Time [s]

Fig. 3. Results of the hydrogen property analysis (a) TDS measurements; (b) isothermal TDS measurements.

(a)

(b)

Fig. 4. (a) Hydrogen concentration profile at the start of the tensile tests, diffusivity obtained from tests in Fig. 3; (b) Engineering stress – engineering strain curves for hydrogen charged and reference tests, 3 repetitions for each condition.

Fig. 5 and Fig. 6 show images of the fracture surface of specimens tested in reference and hydrogen precharged condition, respectively. The full fracture surface of the reference specimen showed ductile dimples formed by microvoid coalescence. The chromium oxide inclusions were located within the larger dimples on the fracture surface. When hydrogen was precharged to the HEA, a changing fracture behaviour was observed as a function of the distance to the edge. Closest to the edge, intergranular fracture was observed with clear indications of slip on the faces. Moving more towards the center of the specimen, mixed fracture types were observed with quasi-cleavage fracture prevailing. At a distance of about 120 µm, a similar fracture appearance as the reference sample was present, i.e. ductile dimples. To interpret this transitional fracture behaviour, the hydrogen concentration profile was plotted as an overlay to the SE image. It is clear that the local hydrogen content determined what fracture mechanism occurred. The higher the hydrogen concentration, the more tendency towards the intergranular type of fracture. This can be understood in terms of the hydrogen enhanced decohesion (HEDE) mechanism in which a sufficiently high hydrogen concentration was present at the grain boundaries. Since clear indications of plastic deformation were still observed, the hydrogen enhanced localised plasticity (HELP) mechanism probably played a minor role as well leading to impingement of