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

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 ~1 at. % Ni. Increasing the concentration of steel ER 321 to 25 and 50 vol. %, leads to complete suppression of the β′-phase, α-Fe(Cr) grains are formed, within which fine particles with a β′/AlNi core/shell structure are observed (Fig. 2, d, e). In this case, in the α-Fe(Cr) solid solution, the precipitation of the dispersed particles of the κiv-phase is observed, the average size of which increases with increasing concentration of steel in aluminum bronze [13]. If the ratio CuAl9Mn2 : ER 321 reaches 25 : 75, a three-phase structure is formed, consisting of 44 vol. % of γ-Fe phase, 32 vol. % of the α-Fe phase and 24 vol. % of the α-Сu phase (Fig. 2, f). Nonequilibrium cooling conditions lead to the precipitation of the dispersed secondary particles of copper and NiAl in the γ-Fe and α-Fe grains, respectively [16]. Static tensile tests have shown that yield strength and an ultimate strength for CuAl9Mn2 and ER 321 are 148 and 440 MPa, and 300 and 610 MPa, respectively (Table 1). Acomposite produced using a volume ratio CuAl9Mn2 : ER 321 = 90 : 10 shows the values of the yield strength and ultimate strength that are comparable to the steel, but much greater than those of the aluminum bronze (Table 1). Addition of the stainless steel up to 50 vol. % into the aluminum bronze during EBAM processing leads to the higher values of the yield strength and tensile strength than those of the CuAl9Mn2 and ER 321 (Table 1). At the same time, in the composite with the ratio CuAl9Mn2 : ER 321 = 25 : 75, a decrease in the yield strength and strength is observed by 240 and 160 MPa, respectively, compared to the composite CuAl9Mn2 : ER 321 = 50 : 50. However, the ER 321 steel, diluted with aluminum bronze, shows improved mechanical characteristics compared to the pure ER 321 steel (Table 1), that are similar to the properties of the composites based on 316SS and tin bronze [1]. The microhardness of the CuAl9Mn2/ER 321 composites increases from 1.4 GPa to 2.33 GPa when the volume fraction of the stainless steel increases up to 50 vol. %. In the case of the CuAl9Mn2/ER 321 composites exhibiting a volume fraction 25:75, the microhardness decreases to 2.16 GPa (Table 1). Assessment of the corrosion properties of the composites by means of voltamperometric methods Fig. 3 shows cyclic voltammograms (CVs) demonstrating reversible redox reactions and irrever- sible anodic processes occurring on the surface of the working electrodes. Anodic oxidation of the metals Fig. 2. Microstructure of CuAl9Mn2 (a), ER 321 (b) and composites with a ratio of CuAl9Mn2 : SS321 = 90 : 10 (c), 25 : 75 (d), 50 : 50 (e) and 25 : 75 (f)

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