Influence of grain boundary modifier on the strength size-dependence displayed by complex-shaped nanocrystalline nickel pillars

Size-dependent softening characteristics of electrodeposited solid core, hollow, C-shaped, and x-shaped nanocrystalline (nc) nickel pillars with outer diameters of ~ 520 nm were investigated by using uniaxial micro-compression techniques. Flow stress results show that only complex-shaped pillars with an average grain size of ~ 9.4 nm prepared with saccharine containing electrolytes soften with decreasing sample sizes and volume-to-surface area ratios. Interestingly, large grain (~ 18.2 nm) specimens prepared with saccharine-free electrolytes do not exhibit this softening behavior. Size-dependent softening may be due to the enhanced grain boundary-mediated deformation in the small grain pillars caused by segregation of the electrolyte additives at the grain boundaries.