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

International audience; We have investigated the partitioning of solutes at crystal defects in intergranular Cr-rich M2B borides after creep at 850°C/185MPa and annealing at 850°C for approximately 3000 hours in a polycrystalline nickel-based superalloy. Borides were found to coarsen in both cases, with the borides after creep to be the thickest (800-1100nm), compared to borides annealed in the absence of external applied load (400-600nm). 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 is systematically 2 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.