Evolution of Y₂O₃ dispersoids during laser powder bed fusion of oxide dispersion strengthened Ni-Cr-Al-Ti γ/γ’ superalloy

The successful synthesis of oxide-dispersion-strengthened (ODS) alloys via laser powder bed fusion (L-PBF) requires a better understanding of the interaction of the oxide dispersoids with the metallic melt pool. Here, a γ/γ’-strengthened Ni-8Cr-5.5Al-1Ti (wt%) model alloy is studied, as a simplified version of the commercial CM247LC alloy, by melting pre-alloyed powders in which 0.5–1 wt% Y₂O₃ nanoparticles were added via mechanical alloying. The Y₂O₃ nanoparticles follow three distinct paths. First, the strong affinity between Y₂O₃ and Al leads to the formation of Y₄Al₂O₉ slag which floats on the melt pool; if in excess, the slag leads to vertically aligned mm-size cavities, preventing complete consolidation of the alloy. Second, a high number density of oxide nanodispersoids is distributed within the alloy's grain inducing a strong (100) texture and noticeably reduces grain size compared to the unmodified base alloy. Third, despite the high stability of Y₂O₃, the extreme temperatures achieved in the melt pool decompose some of the Y₂O₃ precipitates leading to the formation of Ni- and Y-rich particles (16 nm in radius) and Y segregation to the alloy's grain boundaries. The local composition on cracked grain boundaries is consistent with Ni₁₇Y₂ having an embrittling and liquation effect. Based on these results, the critical role of Al in reacting with oxide nanodispersoids during L-PBF manufacturing is discussed, and various types of potentially more successful dispersoids are suggested.