Corrosion properties of CuAl9Mn2/ER 321 composites formed by dual-wire-feed electron beam additive manufacturing

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 The studies of the electrochemical (corrosion) properties of the specimens were carried out by voltammetry and electrochemical impedance spectroscopy (EIS) using a potentiostat-galvanostat PalmSens 4. The electrochemical cell was a three-electrode system in which the specimen under study served as the working electrode. A silver chloride electrode filled with 1 M KCl was used as a reference electrode. The auxiliary electrode was a graphite electrode. In the method of a linear polarization, the following parameters were set: potential range varied from -0.5 to 0 V, scan rate was 1 mV/s. In the cyclic voltammetry (CV) method, the scan rate was 20 V/s, and the potential varied from -1.2 V to +1.2 V. Using the electrochemical impedance spectroscopy (EIS) method, the electrochemical processes associated with a charge (ions, electrons) transfer and diffusion of charges in the electrical double layer were identified. Processing of EIS results was carried out by modeling equivalent electrical circuits that describe the impedance behavior of the “electrolyte/composite” system. For impedance measurements, the DC voltage (Edc) was set equal to the open circuit potential. The amplitude of the sinusoidal signal (Eac) was 0.01 V. The frequency range was varied from 0.1 to 105 Hz. All measurements were performed at 3.5 wt. % NaCl. Pearson’s criterion (χ2), used to fit the raw data, ranged from 10-3 to 10-4, and the fitting errors did not exceed 10 %. PSTrace 5.8 software was used to calculate corrosion parameters. Quantitative assessment of the polarization resistance (Rp) of the composites was done by the Stern-Geary equation: ( ) = β β β + β p a c corr a c ( ) 2.303 ( ) , R i where βa is the slope of the anodic branch; βc is the slope of the cathodic branch; icorr is the corrosion current density. The surface morphology of the specimens after CV measurements was analyzed using a LEO EVO 50 scanning electron microscope (Zeiss, Germany) equipped with an energy dispersive spectrometer INCA Energy (Oxford instruments, UK). Results and Discussion Structural-phase state and mechanical characteristics of the CuAl9Mn2/ER 321 composites Previously, the authors found out the features, associated with formation of the structural-phase states in the aluminum bronze, stainless steel and CuAl9Mn2/ER 321 composites obtained by the EBAM method. It has been observed that aluminum bronze produced by the EBAM method is characterized by a columnar dendritic structure [8]. The martensitic β′ phase is located along the boundaries of the α-Cu grains (Fig. 2, a). The microstructure of the additively manufactured stainless steel ER 321 is characterized by elongated austenite grains exhibiting long and straight dendritic colonies (Fig. 2, b) [17]. Along the grain boundaries of the γ-Fe phase the δ-Fe phase is revealed (Fig. 2, b). When the volume ratio CuAl9Mn2 : ER 321 of the composite is 90:10, the structure of the composite, in comparison with the aluminum bronze, possesses a smaller size of the α-Cu grains, while the volume fraction of the β′ phase decreases significantly. Also, a precipitation of the globular α-Fe(Cr) particles and dispersed particles of the κiv-phase (Fe3Al) are observed (Fig. 2, c) [13]. The α-Cu solid solution contains Fig. 1. Scheme of EBAM process for composites and test specimens cut-up sketch: 1 – electron beam gun; 2 – electron beam; 3 – wire feeders; 4 – ER 321 wire; 5 – CuAl9Mn2 wire; 6 – melt pool; 7 – specimen for structural studies; 8 – specimens for tensile test; 9 – specimen for corrosion testing

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