Effect of yttrium oxide on the microstructure and properties of the VZh159 alloy produced by selective laser melting

This study investigated the effect of adding 1 wt. % yttrium oxide (Y₂O₃) nanopowder on the density, microstructure, and mechanical properties of the VZh159 nickel-based superalloy produced by selective laser melting (SLM). Specimens were fabricated using a 3DLam MINI system equipped with an ytterbium fiber laser with a maximum power of 300 W under ten processing conditions spanning a volumetric energy density E_V range of 74–169 J/mm³. Density was determined by hydrostatic weighing, microstructure was examined by scanning electron microscopy (SEM), and Vickers microhardness and room-temperature tensile properties were measured both in the as-built condition and after heat treatment (solution heat treatment followed by aging). The results showed that the Y₂O₃ addition narrow the optimal processing window: a maximum relative density of 99.5 % was achieved at E_V ≥ 127 J/mm³, compared with 99.8 % at 83 J/mm³ for the unmodified alloy. In the as-built condition, Y₂O₃ has virtually no effect on ultimate tensile strength (Δσ_u < 1 %) but reduced elongation from 35.9 to 30.6 %. After heat treatment, the VZh159 + 1 % wt. % Y₂O₃ composite exhibited 10 % higher yield strength by (865 vs. 787 MPa), 4 % higher ultimate tensile strength by (1170 vs. 1122 MPa), and 57 % higher elongation (15.5 vs. 9.9 %) than the unmodified alloy. The following mechanisms are considered: dendrite refinement through heterogeneous nucleation, grain-boundary pinning during heat treatment via the Zener mechanism, and dispersion strengthening.

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