Abstract
Phosphorus segregation at grain boundaries (GBs) in Ni–P nanocrystalline (NC) thin films has been demonstrated to impede grain growth at elevated temperatures. In this study, we investigate the impact of phosphorus segregation in Ni-1at.%P and Ni-4at.%P alloys on their hardness by using nano-indentation and post-mortem transmission electron microscopy to characterize deformation-induced microstructural changes. The NC film exhibited approximately 20% higher average hardness values when phosphorus was in solution, as a result of the as-deposited processing, compared to films that underwent subsequent thermal annealing to stabilize the grain size by partitioning the phosphorus to the GBs. Under various strain rate loading conditions, the deformation was determined to be GB-mediated control. The effects of phosphorus partitioning on intragranular and GB deformation mechanisms were evaluated using atomistic simulations. While larger grain sizes shift deformation accommodation to intragranular mechanisms, the reduction of the GB fraction with increasing grain size can increase the available solute concentrations in the boundaries leading to active GB-mediated deformation. This interplay between solid solution strengthening, solute partitioning, grain size, global and local solute concentration, and deformation is discussed in detail.
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