PSI - Issue 59

V.V. Lytvynenko et al. / Procedia Structural Integrity 59 (2024) 372–377 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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a free package for modelling FreeFem++. Graphical results were obtained by analyzing and visualizing data in Python.

Fig. 1. (a) Photo of the surface of ¼ symmetric part of the sample after irradiation; (b) schematic illustration of the different zones in the trace of the beam: 1 – quenched re-melted zone, 2 – re-melted & heat-affected zone, 3 – base reference material, 4 - pile up of melt. 3. Results After the HCEB irradiation of the target sample, the surface in the epicenter of irradiation has a structure typical to cast metal, with melt or droplets spread across the surface in a thin layer (see Fig. 1a). In the periphery of the beam’s trace, the surface is smoother but with less pronounced melting. In contrast to the epicenter, melting did not reach deep volumes into the bulk but just slightly modified the surface. The crater depth was around 0.5 mm. Important, we did not study appearance of micro-craters in this for this sample as in Bryukhovetsky (2023). Ablation material condensed from the center of the crater back on the periphery. The radial distribution or propagation of the ablation mater was not high as sings of condensation were not found further than 10 mm from the beam’s trace. Between epicenter and periphery, a crater brustver area was formed which is effectively a pile-up of the melt at the periphery of the crater. In the cross-section of the crater vicinity, we can define distinct zones (see Fig. 1b) of the quenched re-melted zone (with thickness of 50- 150 µm ) and the heat-affected zone (with thickness up to 1 mm) compared to the non-irradiated material. In the quenched area, the driving factors where ablation loss, re condensation and high cooling rates after irradiation, meanwhile the heat-affected zone was less subjected to high cooling rates from external environment while still being under a thermal influence of the beam exposure and heat flow. The fractographic analysis of the cross-section confirmed formation of a heterogeneous microstructure in the near-surface area (see Fig. 2). The reference material has a rough fracture surface with different voids and dimples over the transgranular area. It is characterized by a ductile failure mechanism in general. Heat-affected zone (Fig. 2b) has a lamellar morphology with grain alignment along the direction of thermal flow. The fracture surface is relatively flat. Elongated crystallites emerge through primary crystallization during the solidification process from the liquid phase, and influenced by the thermal flow penetrating the bulk material and a tangent component of mass transfer. The quenched re-melted zone is represented of the similar lamellar microstructure as in the heat-affected zone but it is a disoriented structure due to relaxation of the compression stress during cooling. It has microstructure with cracks and lamellas misaligned to the direction of thermal flow.

Fig. 2. SEM images of fractures of the VT1-0 alloy in (a) re-melted quenched, (b) heat-affected and (c) non-irradiated base reference zones.