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.