OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 The average size of the particles in the specimen is 11.4 nm with a density of f = 2.2×1010 cm−2 as analyzed through transmission electron microscopy (DF) in fi g. 1. The homogenization annealing process resulted in particles mostly ranging from 1.6 nm to 13.3 nm, indicating a prevalence of fi ne phases in the specimen. However, there are also some coarse particles exceeding 25 nm in size. In fi gure 1 a one can clearly observe superstructural refl ections L12; this fact, according to [32], indicates the presence of Al3Sc particles in aluminum alloys containing scandium. The size range of particles in the 1570 0.5Hf alloy is dominated by particles that are between 5.2 and 14.5 nm in size (as shown in fi gure 2, b). However, particles larger than 25 nm are also identifi ed in DF images. The average particle size in this alloy is 10.5 nm, with a particle distribution density of 2.6×1010 cm−2. It is observed that the non-uniformity of particle distribution inside the grain volume was reduced when compared to the 1570 alloy. Although superstructure refl ections are present (as shown in fi gure 2, a), it is relatively weak compared to the original 1570 alloy. This means that a smaller amount of dispersed phases is formed. It is important to note that previous studies showed that in the as-cast 1570 alloy, discontinuous decomposition resulted in the formation of some 7–10 nm Al3Sc nanoparticles. However, discontinuous decomposition is not observed in the alloy with hafnium addition, and Al3Sc particle formation does not occur. By comparing the study results for the as-cast state and after homogenization with the data presented in the paper [29], it can be concluded that heating at 440 °С for 4 hours increases the general number of nanoparb Fig. 2. Fine structure of the cast billet made of alloy 1570 0.5Hf after its homogenization annealing at 440 °C for 4 hours: а) microdiff raction in the zone of axis [001] α; b) DF а
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