Secotom

A Mg-Y-RE-Zr based magnesium alloy (WE43MEO, Meotec GmbH, Aachen, Germany) nominally containing app. 4% yttrium, 3% Rare Earths and less than 0.6% zirconium with magnesium being the remainer was included in this study. Samples were cut-grinded from a rod (Secotom, Struers GmbH, Willich, Germany), followed by chemical polishing in nitric acid (HNO₃) (65% in volume). The samples with a final diameter of 18.8 mm and 0.2 mm height were washed in water and ethanol and preserved in a dry-air closet to prevent further oxidation. Prior to the degradation experiments, test samples were degreased in an ultrasonic bath of ethanol for 10 min. Mg WE43 samples further underwent PEO treatment in a stainless-steel container forming the counter-electrode. A layer thickness of 9 +/− 6 µm was targeted for both PEO variants by adjusting current density between 1.35–3.5 A/dm² and the corresponding treatment time between 8–25 min. As electrolytes, two phosphate-rich electrolytes supplemented with different conductivity agents were used (Table 2). For each experiment, n = 11 test samples of Mg WE43 and the two types of PEO treatments (PEO-A and PEO-B) were used each.

Commercially available 5Y zirconia powder containing 0.05 wt% of alumina (Zpex Smile, Tosoh, Tokyo, Japan) was used for a starting powder. The powder was pressed uniaxially by a press molding machine (Sansho Industry, Osaka, Japan) to obtain zirconia blocks having a diameter of 19 mm × thickness of 19 mm and discs having a diameter of 100 mm × thickness of 17 mm. Next, the blocks and discs were isostatically pressed at 200 MPa using a cold hydrostatic isotropic press (Sansho Industry, Osaka, Japan).
The pressed zirconia blocks/discs were degreased at 500 °C in an inert gas oven (INH-21CD, KOYO THERMO, Nara, Japan) and then fired in a firing furnace (SC-3035F, MOTOYAMA, Osaka, Japan) at 970 °C to obtain a pre-sintered zirconia block/disk (φ18 mm × 18 mm/φ98.5 mm × 16 mm).
The pre-sintered zirconia blocks and disks were cut with cutting equipment (Secotom, Struers, Ballerup, Denmark), and surface polished with SiC water resistant polishing paper (# 1000) to reach the dimension required by each test.