Record-breaking strength and solid solution softening in Ni and Ni₃Fe nanoparticles

We demonstrate that faceted single-crystalline Ni nanoparticles produced by solid-state dewetting from a sapphire substrate exhibit an ultrahigh compressive strength (up to 34 GPa) unprecedented for crystalline metals. This strength is consistent with all available estimates of the theoretical strength of Ni. Three factors are responsible for this record-high strength: (1) large shear modulus of Ni (78 GPa), (2) smooth edges and corners of the nanoparticles that reduce the stress concentration during the compression, and (2) thin oxide layer on the particle surface that softens the contacts with the substrate and indenter. This experimental discovery is augmented by molecular dynamics simulations that closely mimic the experimental conditions, including the degree of particle roundness, the softening of the particle contacts with the substrate/indenter, and the testing temperature [1]. We also demonstrate that doping Ni nanoparticles with Fe significantly decreases their strength. This counter-intuitive solid solution softening is attributed to the local misfit stresses around the solute atoms promoting the nucleation of dislocations.

References

1. A. Sharma, J. Hickman, N. Gazit, E. Rabkin, Y. Mishin, Nickel nanoparticles set a new record of strength, Nature Communications 9 (2018) 4102