Influence mechanisms of Y2O3 addition on the microstructure and wear resistance of laser-cladded T-800 + Si coatings on DD5 substrates

Abstract

This study investigates the effects of adding varying contents (0, 1, and 2 wt%) of micron-sized Y₂O₃ particles on the microstructure and wear resistance of laser-cladded T-800 + Si coatings. Through BSE, EDS, EBSD, microhardness tests, and wear resistance evaluations, the influence mechanisms of Y₂O₃ addition on the precipitation behavior of Laves phases and secondary phases, grain growth, dislocation distribution, microhardness, and wear resistance were systematically elucidated. The optimal Y₂O₃ addition content was determined. The results show that with 1 wt% Y₂O₃ addition, grain refinement is most pronounced, reducing the average grain size by 12.17 % to 4.34 μm compared to the coating without Y₂O₃ (4.93 μm). The moderate Laves phase content (55.1 %) and the formation of Y₅Si₃ secondary phase particles were observed. The average KAM value increased to 0.40° with a more uniform distribution. These features, combined with grain refinement, Laves phase, Y₅Si₃ precipitation, and dislocation strengthening, resulted in the highest average microhardness (803.4 HV_0.5), a 10.19 % increase compared to the coating without Y₂O₃ (729.1 HV_0.5). Additionally, the dense oxide film contributed to superior wear resistance, with the wear volume loss and wear rate reduced by 34.98 %. At 2 wt% Y₂O₃, despite higher Laves phase content (67.5 %) and KAM value (0.75°), grain coarsening (4.84 μm) due to Ostwald ripening and rare-earth polarization effects weakened the strengthening mechanisms, reducing microhardness to 764.9 HV_0.5. The discontinuous oxide film further compromised wear resistance, though it remained better than the coating without Y₂O₃.