Fine microstructure, better compactness, and significant fracture toughness of multi-component Nb–Si based alloy by an appropriate amount of Yttrium addition during the laser melting deposition

During the rapid solidification of laser melting deposition, poor melt pool fluidity in Nb Si based alloys results in insufficient pore wetting and filling, significantly degrading the mechanical properties. To address this issue, controlled addition of rare earth Yttrium (Y) was utilized to improve melt fluidity, thereby enhancing the density of the deposited layer and optimizing mechanical properties. Results show that an appropriate Y (0.15 at.%) addition increased sample density from 99.83 % to 99.97 %. Y addition did not alter the primary phase constituents of the alloy, which remained Nbss, α-Nb 5 Si 3 , and γ-Nb 5 Si 3 phases, but it affected the phase fractions. With the increase of Y content, the total silicide content increased in the alloys, alongside the precipitation of more nanoscale Y 2 O 3 and γ-Nb 5 Si 3 phases. The alloy with 0.15 at.% Y addition achieved maximum fracture toughness of 15.13 MPa·m 1/2 due to microstructure refinement and compactness improvement. For compressive strength, a continuous enhancement was observed up to 2358.9 MPa in alloys with 1.0 at.% Y addition, which was attributed to increased silicide content, the enhanced solid solubility of Y in the Nbss phase, and the increased content of nanoscale Y 2 O 3 and γ-Nb 5 Si 3 precipitates.