OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 2 2024 phase lamellas is observed with coarsening Mg24Y5 particles, i.e., the length grows from 0.3 to 0.8 µm and the width expands from 0.04 to 0.07 µm (Fig. 3, e). The average cross-sectional dimension of b′-phase precipitates is 0.2 µm (Fig. 3, f). It is notable that the length and width of smaller b1-phase lamellas localizing nearby the grain boundaries, vary from 0.3 to 0.8 µm and from 0.02 to 0.08 µm, respectively. It is worth noting that according to [24], the formation of b1-phase lamellas is determined by the presence of b′-phase globules. TEM observations [23] revealed b′-, and b1-phases precipitates in the Mg-Y-Nd system alloy after annealing at 250 °С. The latter led to the formation of metastable b′-, and b1-phases followed by the formation of the equilibrium β-phase. It is shown that the b1-phase represented b′-phase nuclei and could generate much shear energy and shear energy accommodation. During a long-term annealing, e.g., aging at 250 °С, the b1-phase transferred to the equilibrium β-phase. Annealing at 350 °С provides the width expansion of continuous subgrain boundary in the range of 0.8 to 1.7 µm (Fig. 3, g). The average length and width of b1-phase lamellas are respectively 0.6 and 0.03 µm. The average size of b′-phase precipitates is 0.2 µm, as it is demonstrated in Fig. 3, h. Annealing at 350 °С promotes aggregation of Mg24Y5 intermetallic particles. Annealing at 450 °С results in widening of the eutectic b-phase network up to 2 µm. In this case, most of Mg24Y5 particles are tetrahedrons having the medium size of 1.3 µm. Localized regions consist of typiFig. 3. Bright field TEM images with corresponding microdiffraction patterns of extruded Mg-2.9Nd-1.3Y alloy microstructure after annealing at: a, b – 100 °С; c–f – 300 °С; g, h – 350 °С; i, j – 450 °С a b c d e f g h i j
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