Nanoscale room temperature creep of nanocrystalline nickel pillars at low stresses

Nanoscale time-dependent plastic deformation (creep) behavior of nanocrystalline (nc) Ni, at low stresses and at room temperature, was systematically explored through uniaxial creep experiments performed on nano-/micro-pillars (with diameters of 600, 1000, and 2000 nm). It was revealed that the creep indeed occurs at ambient temperature, and exhibits a creep strain of ∼2 × 10−4–9 × 10−3 (for 200 s load-holding) at stresses below the nominal yield strengths of the pillars. At a given stress, much higher total creep strains and strain rates accrue in the smaller pillars, which is likely due to the increased contributions of free surfaces. Estimation of the stress exponent and the activation volume suggests that the nanoscale creep event under low stresses may be dominated by diffusion-controlled mechanisms such as free surface assisted grain-boundary diffusion and grain-boundary sliding.