PSI - Issue 51

3

Nils Wegner et al. / Procedia Structural Integrity 51 (2023) 122–128 N. Wegner et al. / Structural Integrity Procedia 00 (2022) 000–000

124

Fig. 1. (a), (b) Cross section of WE43 with EDS mappings of (c) Nd, (d) Y, (e) Zr; PEO layer: (f) top view, (g) cross section (Wegner et al., 2022).

This study refers to published results (Hartjen et al., 2021). In three-week immersion tests at open circuit potential (OCP), the specific hydrogen volume V H2,spec was detected for both materials and was used to calculate the corrosion rates m � corr (Equation 3). Based on V H2,spec , the results were divided into three periods, each with an approximately constant HER and, thus, constant corrosion rate (Table 1). In a second study, the relationship between the corrosion rate and current density i (for galvanostatic polarization (GSP)) was investigated for embedded samples of WE43. Since only the cross section was considered for this sample type, this case was defined as two-dimensional (2D). According to Wegner and Walther (2021), Equation 4 gives a relationship between the current density and the corrosion rate. Using this relationship, the present investigations aimed to simulate the three-week immersion tests by applying GSP achieving the same mass loss (m corr = m � corr ∙ t → m � corr ,0 ∙ t 0 = m � corr ,GSP ∙ t GSP ) after a shortened time t GSP as after the initial immersion time t 0 . Through this assumption, the calculation of the current density required to achieve a defined corrosion rate is enabled (Equation 4). Table 1. Data for the design of immersion tests with GSP on WE43 (PEO) (Hartjen et al., 2021; Wegner and Walther, 2021; Wegner et al., 2022). Material Corrosion rate m � corr (10 3 mg cm -2 a -1 ) Time interval (h) Current density i (mA cm -2 ) t 0 t GSP WE43 0.21 0-114.4 0-16.3 1.05 0.12 114.4-241.5 16.3-34.5 0.61 0.18 241.5-504 34.5-72 0.94 WE43 PEO 0.15 0-111.6 0-15.9 0.77 0.07 111.6-268.5 15.9-38.4 0.41 0.09 268.5-504 38.4-72 0.51 � ����,��� ��10 ����� ∙ ����� � � �� � � ����,� ∙ � � � ��� ∙ 10 ������ ����� (4) The test setup enabled the application of GSP through a three-electrode system within a corrosion cell and the detection of hydrogen gas through a eudiometer. The specimen acted as working electrode, graphite as counter electrode, and an Ag/AgCl electrode with Haber-Luggin capillary as reference electrode. The polarization was controlled by a PCI4300 potentiostat (Gamry Instruments, Warminster, PA, USA). A 0.9% NaCl solution (36.5 °C) was used as electrolyte. The aim was to reproduce the corrosion of the three-week immersion tests in three days. Using Equation 4, m � corr of the initial condition and a time factor of 7 (t 0 /t GSP = 21/3), the current densities were calculated (Table 1). The tests were carried out intermittently, pausing the tests and changing the electrolyte after 24 h. µ-Computed tomography (µCT) scans of the gauge length were performed to evaluate the macroscopic corrosion morphology. A X TH 160 µCT system (Nikon, Tokyo, Japan) with a maximum accelerating voltage of 160 kV was used. The scans were performed with a beam energy of 105 kV, a beam current of 55 µA, an exposure time between