Effect of pH on corrosion behavior of CuCrZr in solution without and ...

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2. Experimental details Wrought cylindrical bars <strong>of</strong> precipitation-hardened high copper alloy CuCrZr (C18150) was selected for present study. Annealed Cu (C11000) and precipitation-hardened CuCr (C18200) and CuZr (C15000) were included for comparison purpose and for exploring the role <strong>of</strong> the alloying elements on the corrosion behavior <strong>of</strong> the alloys. Disc specimens <strong>of</strong> diameter <strong>of</strong> 13 mm and thickness <strong>of</strong> 10 mm were prepared by a cut-<strong>of</strong>f machine with coolant. The Vickers hardness <strong>of</strong> the specimens was determined using a microhardness tester at a load <strong>of</strong> 200 g and a loading time <strong>of</strong> 10 s. The designation, chemical compositions, and Vickers hardness <strong>of</strong> the tested specimens are shown in Table 1. Prior to the corrosion tests, the specimens were mechanically ground by CAMI 800-grit silicon carbide paper, degreased in alcohol, rinsed in distilled water, and finally dried in a cool air stream. To investigate electrochemical corrosion behavior, the specimens were embedded in cold-curing epoxy resin. Epoxy resin was also applied at the interface between the specimens and the mount in order to avoid crevice corrosion as well as to expose a test area <strong>of</strong> 1 cm 2 . In order to avoid the influence due to air exposure, the test solutions were freshly prepared by dissolving 35 g NaCl in 965 ml distilled water and the <strong>pH</strong> was varied by adding H 2 SO 4 or NaOH. Open-circuit potential (OCP) measurement and potentiodynamic polarization test in the freshly prepared solutions without and with 0.6 M NaCl at <strong>pH</strong> values <strong>of</strong> 1, 3, 5, 7, 10 and 12, open to air at 25±1 o C, were performed in a three-electrode cell in a water bath using a PAR VersastatII potentiostat according to ASTM Standard G5-94 [8]. All potentials were measured with respect to a saturated calomel electrode (SCE, 0.244 V versus SHE at 25 o C) as the reference electrode. Two parallel graphite rods served as the counter electrode for current measurement. After the OCP measurement for a period <strong>of</strong> 2 hours, the final steady OCP was recorded and then 4
the potential was increased at a rate <strong>of</strong> 1 mV s -1 , starting from 0.2 V below the OCP and terminated at 1 V. From the polarization curves, the corrosion current densities (I corr ) <strong>of</strong> the alloys in various test conditions were determined by the fitting to the linear region using Tafel extrapolation with the aid <strong>of</strong> commercial s<strong>of</strong>tware (PowerCORR, V.2.42). For specimens showing pitting corrosion behavior at high <strong>pH</strong>, the pitting potentials and passive currents were also recorded. The microstructure, morphology <strong>of</strong> the corroded surface, and chemical composition <strong>of</strong> the corrosion products <strong>of</strong> CuCrZr were investigated by scanning electron microscopy (SEM, Hitachi S-3400N) and energy dispersive X-ray spectroscopy (EDX, Horiba EX-250). 3. Results and discussion 3.1 Microstructure The microstructure <strong>of</strong> CuCrZr consists <strong>of</strong> equiaxed, twinned grains <strong>of</strong> alpha copper solid solution as shown in Fig. 1. Typically it had been cooled rapidly so the Cr and Zr remained in solid solution. The precipitation treatment allowed the Cr and Zr to precipitate out <strong>of</strong> the solid solution, forming a dispersion <strong>of</strong> Cr and Zr precipitates throughout the matrix. The precipitates <strong>of</strong> Cr and Zr are too fine and invisible at low magnification. 5
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Page 17 and 18: Table and Figure captions Table 1.
Page 19 and 20: Designation UNS number Hardness (Hv
Page 22 and 23: Fig. 1 Fig. 1. SEM micrograph <stro
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Page 36: Fig. 14 Element O K Cl K Cr K Cu K

Effect of pH on corrosion behavior of CuCrZr in solution without and ...

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