Gradient refinement mechanism of mixed intermetallic particles for an equiaxed K492M superalloy

The gradient refinement mechanism of mixed intermetallic particles on equiaxed K492M superalloy was studied. The grain size of K492M superalloy added with mixed intermetallic (CrFeNb and Co₃FeNb₂) particles could be obviously refined from 3132.89 μm to 608.51 μm while the separate intermetallic (CrFeNb or Co₃FeNb₂) particles led to little refinement. This superior refinement performance was attributed to the synergistic effect of the mixed particles in promoting the formation of highly potent Ni₉Nb phases at the interfaces between the γ matrix and the intermetallic particles. Based on Edge-to-Edge model (E2EM) and orientation identification, the lattice misfit between the γ matrix and Ni₉Nb was about 0.27% with the orientation relationship: (200)_γ || (200) _Ni9Nb, [001] _γ || [001] _Ni9Nb. A gradient refinement mechanism was proposed to elucidate the role of mixed intermetallic particles. Both intermetallic particles facilitated the formation of Ni₉Nb acting as the nucleation sites. However, CrFeNb particles preferentially formed Ni₉Nb due to a higher thermodynamic driving force, followed by Co₃FeNb₂. Consequently, the mixed intermetallic particles provided a greater density of nucleation sites compared to separate additions, leading to enhanced grain refinement.