Microstructure and mechanical properties of FeCrVTa0.1W0.1Tix multi-principal element alloys

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The existing multi-principal element alloys developed for fusion reactor structural applications still face formidable challenges in engineering deployment due to their high activation, insufficient strength, and poor irradiation resistance. To address these issues, we developed a series of FeCrVTa 0.1 W 0.1 Ti x (x = 0–0.4 in relative atomic ratio) low-activation multi-principal element alloys and systematically investigated the effects of Ti content on the microstructure and mechanical properties. The results show that Ti addition progressively transforms the matrix from a single dendritic structure to a mixed dendritic + equiaxed structure, accompanied by a morphological evolution of the Laves phase from lamellar to island-like features. Further analysis reveals that Ti modifies the solute partitioning behavior of Ta and W, inducing constitutional undercooling, which significantly refines the dendritic structure—the secondary dendrite arm spacing decreases from 36.1 μm to 12.6 μm—and the area fraction of the Laves phase increases linearly with Ti content. Regarding mechanical properties, increasing Ti content enhances yield strength but reduces ductility; at x = 0.1, the alloy achieves an optimal strength–ductility synergy, with a yield strength of 1532 MPa and a fracture strain of 16.9%, outperforming most comparable alloys. Quantitative analysis of the strengthening mechanisms reveals that as the relative atomic ratio of Ti increases from 0.1 to 0.2, the dominant strengthening mechanism transitions from grain refinement strengthening alone to a synergistic combination of grain refinement and hetero-deformation induced (HDI) strengthening. This study provides a valuable reference for the compositional design and microstructural regulation of low-activation multi-principal element alloys with combined low activation, high strength, and good ductility for fusion reactor structural applications.