OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 3 2025 Fig. 4 illustrates compressive stress-strain responses of the as-cast and heat-treated alloys. The offset yield strength, compressive strength, and residual strain are presented in Table 4. The as-cast alloy exhibits good strength and plasticity characteristics. Structural transformations in the alloy during heating to 900 °C have little effect on the strength properties of the material but significantly reduce its plasticity. This reduction is attributed to the precipitation of the brittle σ phase in the structure. The authors of [32] also pointed out the effect of decreased plasticity within a similar temperature range of heat treatment. During heat treatment at 1,000 °C and 1,100 °C, a significant increase is observed in the strength characteristics of the alloy. At 1,100 °C, the residual strain also increases. Based on the results of XRD analysis and optical microscopy, it can be suggested that the main reason for this effect is transformations occurring both in the solid solution of the BCC phase (B2-phase dissolution, substructure rearrangement, and an increase in the lattice parameter) and in the eutectic (increase in the proportion of the Laves phase and refinement of eutectic cells). The simultaneous increase in plasticity is likely due to the relief of internal stresses, a reduction in the number of crystalline defects, and coalescence of structural components in dendrites and the eutectic. However, a more precise analysis of this unique effect on the properties of the AlCoCrFeNiNb0.25 alloy requires further research. Fig. 4. Compressive stress-strain curves of the AlFeNiCoCrNb0.25 alloy in the as-cast state and after heat treatment Ta b l e 4 Offset yield strength, compressive strength and residual strain of AlCoCrFeNiNb0.25 alloy in the as-cast state and after heat treatment σ0.2 (MPa) σu(MPa) ɛ (%) Т30 1356 1962 7.7 Т900 1605 1894 2.8 Т1000 1502 2438 9.8 Т1100 1369 2494 16.4 Conclusions Doping of the AlCoCrFeNi high entropy alloy with niobium in a molar ratio of 0.25 led to the stabilization of the solid solution based on the body-centered cubic (BCC) phase both in the as-cast state and after heat treatment involving heating to 900 °C, 1,000 °C, and 1,100 °C followed by air cooling. The resulting structure of the alloy, regardless of the heat treatment modes, consisted of dendrites of the solid solution and a eutectic with the Laves phase in the interdendritic space. Heat treatment altered the phase composition of the alloy and improved its structural components. Upon heating to 900 °C, alongside the already formed solid solution and Laves phase, the σ phase precipitated in the structure, which increased the microhardness of the alloy. However, this did not improve the strength properties due to the low plastic characteristics of the σ phase. The strength characteristics of the alloy significantly increased during heat treatment at 1,000 °C and 1,100 °C. At 1,100 °C, the residual strain also rose. The main reasons for this effect may include
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