Intentional and unintentional elemental segregation to grain boundaries in a Ni-rich nanocrystalline alloy

Grain boundary segregation is an important phenomenon for nanocrystalline materials as it influences thermal stability and mechanical properties. While several studies have considered effects of single, intentional segregants, co-segregation of intentional and unintentional segregants to general grain boundaries is not commonly investigated using experimental techniques on the atomic scale. This study utilized aberration-corrected scanning transmission electron microscopy and atom probe tomography to evaluate the grain boundary structure and chemistry of an electroplated and annealed electrodeposited Ni–W alloy. Several phases were observed in the annealed microstructure including elongated nanoscale oxide particles and relatively large impurity carbide phases. Furthermore, grain boundaries regularly exhibited ordered structures, minimal elemental tungsten segregation (intended solute) and impurity carbon segregation (unintentional solute), but moderately high-impurity oxygen segregation (unintentional solute). The unintentional segregated impurities (oxygen and carbon) resulted in a total average grain boundary composition of ~ 10 at.%. The consequence of impurity segregation is discussed in terms of thermal stability and potential mechanical properties.