Partitioning of Solutes at Crystal Defects in Borides After Creep and Annealing in a Polycrystalline Superalloy

We have investigated the partitioning of solutes at crystal defects in intergranular Cr-rich M2B borides after creep at 850 degrees C/185MPa and annealing at 850 degrees C for approximately 3000 h in a polycrystalline nickel-based superalloy. Borides were found to coarsen in both cases, with the borides after creep being the thickest (800-1100 nm), compared to borides annealed in the absence of an external applied load (400-600 nm). Transmission electron microscopy revealed that the coarsened borides have either a tetragonal I4/mcm structure, or an orthorhombic Fddd, with those two structures coexisting in a single particle. The presence of a very high density of planar faults was systematically observed within the coarsened borides. The faults were correlated with chemical fluctuations of B and Cr, revealed by atom probe tomography. In addition, partitioning of Ni and Co was observed at dislocations within the borides after creep, providing insights into the deformation of borides.

Automated summary

Solute partitioning in Cr-rich M2B borides at crystal defects was investigated after creep and annealing in a nickel-based superalloy. Coarsening of borides was observed in both cases, with the coarsened borides after creep being the thickest. The presence of a high density of planar faults and chemical fluctuations of B and Cr within the coarsened borides were revealed by transmission electron microscopy and atom probe tomography.