The dissolution/evolution of yttria in IN718 ODS superalloy powders during high energy attritor milling and subsequent SPS consolidation

In the development of ODS Ni-based superalloys the dissolution/evolution of yttria during mechanical alloying and subsequent consolidation is an unexplored and scarcely reported area. In the present investigation, the dissolution/evolution of yttria (0.7 wt.%) in IN718 ODS superalloy powder was investigated during mechanical milling and subsequent spark plasma sintering. In the course of milling yttria is likely to combine with elements like Al and Ti, forming a supersaturated solid solution of Y-Al-O and Y-Ti-O type oxide clusters (according to the formation of enthalpy) possibly in the partially amorphous state and dissolved at lattice defect sites. After providing heat, a supersaturated solid solution of Y-Al-O and Y-Ti-O type oxide-clusters transform from partial amorphous to highly stable crystalline Y₄Al₂O₉ and Y₂Ti₂O₇ oxide clusters.