Microstructure effects on corrosion behaviour of Mg-1Ca alloy in Ringer’s solution
Description
Information regarding corrosion properties of coarse grained (CG), ultrafine-grained (UFG) and nanocrystalline (NC) Mg-1Ca alloy. These includes XRD, AFM, PDP, EIS data and weight loss information
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A binary Mg-1Ca alloy was used. The as-supplied cast samples were homogenised at 450±5 °С for 12 hours. To produce nanostructured samples, 20 mm diameter disks were subjected to high-pressure torsion (HPT) treatment at room temperature. To assess the effect of the grain size, the nanostructured samples were annealed at 250±5 °С for 6 hours. This heat treatment provided ultrafine-grained structure in the samples. Thus, three types of the alloy were assessed: coarse-grained, nanostructured (nanocrystalline) and ultrafine-grained, denoted as CG, NC and UFG respectively. The phase composition was characterised by X-ray diffractometer Rugaku Ultima IV in Cu Kα radiation at 40 kV and 40 mA. Further, the XRD spectra were processed using Philips X’Pert Highscore Plus software with PDF2 pattern database. Rietveld analysis was employed in order to evaluate the quantitative amount of the crystalline secondary phase. A Bruker Multimode 8-HR Atomic Force Microscope (SKPFM) was used to obtain the surface potential maps of the studied alloys. The specimens for characterisation were polished 24 h prior to the measurement and kept in a desiccator to avoid partial oxidation. Corroded specimens were analysed after 24 h of atmospheric exposure. The scanning was carried out in tapping mode at a constant tip-to-sample distance of 150 nm. Corrosion properties were assessed using weight loss and electrochemical techniques. The sample weight was measured using analytical balance GR-200 (A&D, Japan) with an accuracy of 0.1 mg. The samples were immersed into 50 ml of Ringer’s solution (0.86% NaCl, 0.03% KCl, 0.033% CaCl2, pH 7.4) for 32 days at 37±2 °C. The electrochemical tests were carried out also in Ringer’s solution at temperature 37.0±0.2 °С using P-5X (Elins, Russia) electrochemical system. The reference electrode was a silver chloride electrode filled with a saturated KCl solution; the counter electrode was a platinum rod. After the open circuit potential (OCP) was settled within ± 20 mV for at least 30 minutes, the electrochemical impedance spectroscopy (EIS) was performed from 100 kHz to 1 mHz with the magnitude of 10 mV around the OCP. The potentiodynamic polarisation test was run from -300 mV to + 300 mV with respect to the OCP value at a rate of 0.25 mV/s.