PSI - Issue 81

Anatolii Klymenko et al. / Procedia Structural Integrity 81 (2026) 470–477

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Lead residues from the samples were removed chemically using a solution of acetic acid, hydrogen peroxide, and ethyl alcohol in a ratio of 1:1:1. Metallographic studies of the microstructure of the samples were carried out using an optical microscope Leica DMi8 C with a digital camera Leica DMC2900, after their electrolytic etching in chromic anhydride CrO 3 . The structure of the formed corrosion products and their chemical composition were studied using an electronic scanning microscope JEOL JSM-35 CF (Japan) and Tescan MIRA 3 LMU with an energy dispersive spectrometer (EDS) Oxford X-max 80 mm 2 . Corrosion tests of samples were carried out in ceramic crucibles placed in sealed autoclaves to limit oxygen access, at melt temperatures of 450 and 650 °C, with a 24/7 exposure and a duration of 1440 h, with intermediate examination of samples at 240, 480, 720, and 1000 h . The oxygen concentration in the lead melt at 450 °C was 1.92 10⁻⁴ wt.%, and at 650 °C – 6.06 10⁻⁴ wt.%. 3. Results and discussion Alloy structure and corrosion rate Alloy Inconel 601 is a homogeneous single-phase nickel alloy, the structure of the base metal with traces of rolled products consists of equiaxed grains of 5...40 μm (Fig. 1a). Phases commonly present in the microstructure of an alloy include chromium carbides and titanium nitrides. Along the grain boundaries, the precipitation of Ме 23 С 6 carbides is recorded. After testing at 450 °C (Fig. 1b), a single-phase structure with a rounded grain extended along the rolling line can be observed on the base metal. A short period of holding in the melt at a given temperature leads to the strengthening of the metal due to the precipitation of dispersed particles of non-metallic inclusions along the boundaries and inside the grains. A dense and uneven layer of corrosion products is observed on the metal surface. Increasing the duration of exposure in the melt to 720 hours leads to further diffuse strengthening of the metal due to the chaotic precipitation of non-metallic inclusions (Fig. 1с). An increase in the layer of corrosion products is observed and their delamination from the alloy surface occurs. After 1440 hours of exposure in molten lead, the grain size in the alloy did not change and was 4...5 μm in the near-surface layer (Fig. 1d). At a distance of about 10 μm from the surface, an increase in grain size from 5 to 12 μm is observed, and closer to the center of the sample, the grain size increases to 30...50 μm . The grain boundaries have an irregular geometric shape with traces of twinning. At 650 °C, after 240 hours, intensive etching (oxidation) of the surface can be observed on the alloy, which leads to an increase in the layer of corrosion products (Fig. 2a). White inclusions in the layer of corrosion products indicate intensive dissolution of the base metal elements and their diffusion into the layer of corrosion products in the form of individual grains. Increasing the holding time in the melt to 720 hours leads to grain growth and dispersed strengthening of non-metallic inclusions (Fig. 2b). White inclusions in the layer of corrosion products indicate intensive dissolution of alloy elements and their diffusion into the layer of corrosion products in the form of individual grains. Long-term exposure for 1440 hours at 650 °C led to the fact that dispersed inclusions are located both in the volume of the alloy and along the grain boundaries (Fig. 2с). The surface layer undergoes significant changes, the grains acquire an irregular geometric shape, and their size changes from 2 to 10 μm, whil e the thickness of the modified surface layer increases to 10- 12 μm.

Fig. 1. Photographs of the microstructure of samples of Inconel 601 alloy in the initial state (a) and after exposure in lead melt liquid for 240 h (b), 720 h (c) and 1440 h (d) at 450°C.

Fig. 2. Photographs of the microstructure of samples of Inconel 601 alloy after exposure in lead melt liquid for 240 h (a), 720 h (b) and 1440 h (c) at 650°C.