Experiments had indicated that the first yield point of micron-sized metals exhibited significant statistical scatter as well as strong dependence upon the specimen size. In this work, molecular dynamics simulations were carried out to investigate the onset of shear deformation in a small block of material, using an embedded atom potential for the intermetallic Ni3Al alloy. Incipient plasticity in the form of homogeneous dislocation generation was observed to occur at atomic sites with interatomic displacements approaching one-half of the Shockley partial Burgers vector. From the distribution function of the interatomic displacements observed in the molecular dynamics simulations, the probability of a general material volume surviving under given loading conditions was predicted. The survival probability was then calculated for several situations, including homogeneous deformation and nano-indentation, to predict the critical load for incipient plasticity to occur in these situations. The predicted results were compared to micro-pillar compression and nano-indentation experiments on Ni3Al available in the literature.

Size Dependence and Stochastic Nature of Yield Strength of Micron-Sized Crystals: a Case Study on Ni3Al. Ngan, A.H.W., Zuo, L., Wo, P.C.: Proceedings of the Royal Society A, 2006, 462[2070], 1661-81