PSI - Issue 42

Simon Vander Vennet et al. / Procedia Structural Integrity 42 (2022) 813–820

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S. Vander Vennet / Structural Integrity Procedia 00 (2019) 000–000

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Table 1: Compositions (in wt%) and phases of the tested materials

Material C Mn Si

Al

Phases

DP 0.08 0.95 0.13 0.03 Ferrite, martensite (Van den Eeckhout et al. (2020)) TRIP 0.20 1.76 0.72 0.96 Ferrite, bainite, austenite (Escobar et al. (2012)) Q&P 0.22 2.33 1.60 0.05 Ferrite, martensite, austenite (Thomas et al. (2011))

Fig. 1: Schematic overview of the electrochemical permeation method along with the used proof ring (Van den Eeckhout (2019); Depover and Verbeken (2021))

2.2. Hydrogen permeation

Hydrogen permeation was carried out using a set-up based on the Devanathan-Stachurski cell (Devanathan et al. (1962)) modified with an external loading device. The set-up, displayed schematically in Figure 1, consists of two double glass cells, allowing accurate temperature control of the electrolyte, separated by the sample. The choices made during the development of this methodology are elaborately explained in (Van den Eeckhout (2019); Depover and Verbeken (2021)). This method requires the use of rectangular samples with a thickness of 0.85 mm, a width of 25 mm and a length of 90 mm. The surface of this sample was ground on 500 grit SiC paper and the clamped edges were sandblasted to improve surface friction between the clamps and the sample. To apply the load during the per meation test, the sample was first mounted in the proof ring manufactured by CORMET R . After clamping, the tensile load was applied by compressing the ring and the actual force could then be determined from the load amplifier. After mounting the sample between the cells, the sample was connected to the potentiostats on the anodic and cathodic side, using an Ametek Versastat3F and an Ivium CompactStat.h, respectively. The anodic side was filled with deaerated 0.1M NaOH and placed at a potential of -500 mV relative to a Hg / Hg 2 SO 4 reference electrode. After the anodic current density reached a value below 50 nA / cm 2 , the cathodic cell was filled with deaerated 0.1M NaOH and placed under cathodic protection at -3 mA / cm 2 . The oxidation current density versus time was then further measured to determine the hydrogen di ff usion rate and the corresponding apparent di ff usion coe ffi cient ( D app ). In order to minimise the influence of surface e ff ects, D app was determined by fitting the first half of the normalised permeation transient to the analytical solution of Fick’s second law (Archer and Grant (1984)).

2.3. Determination of the yield stress

The tensile stresses imposed varied between 0% to 125% of the yield strength (YS), which was determined by a ten sile test performed following the ISO-6892 procedure (ISO 6892-1:2009 (E)) on an initial gauge length of 80 mm. This tensile test was performed on a Tinius Olsen 50ST tensile machine and was strain controlled at a rate of 0.015 min − 1 . The displacement was measured by an extensometer attached to the sample. The YS was determined using the 0.2% strain o ff set method.