Deformation mechanism maps for sub-micron sized aluminum

Plastic deformation of sub-μm sized metals at different temperatures is influenced by factors absent in their bulk counterparts, including surface diffusion assisted softening and mechanical/thermal annealing-induced hardening. The test temperature and sample size therefore strongly affect the mechanical behavior, necessitating the construction of new deformation mechanism maps (DMM). Here, based on results from in situ quantitative compression tests on micro-pillars at various sizes and temperatures ranging up to 400°C, we have constructed DMMs for single-crystalline sub-micron-scale aluminum, consisting of elasticity, diffusive plasticity, and displacive plasticity regimes. In the sample size-stress DMM (for a fixed temperature), a “strongest size” is found at the triple junction of three regimes, above which “smaller is stronger”, below which “smaller is weaker”. In the diffusive plasticity regime, deformation is localized within the top pillar volume demarcated by a moving front interface, which is likely a newly formed grain boundary, that is impenetrable to impinging dislocations below a critical stress of ∼1 GPa.