October 4-9, 2015
Nanolaminates consisting of alternating layers of two dissimilar materials can possess extraordinary mechanical properties compared to their bulk counterparts, making them promising for engineering applications. Extremely high room temperature strengths and damage tolerance have been reported when the individual layer thicknesses are less than 100 nm, and this has been attributed to the large density of interfaces and grain boundaries that act as barriers for pinned dislocations [1–3]. Micropillar compression tests have been extensively employed to study nanolaminate deformation with the force generally applied perpendicular to the individual layers [1,4,5]. However, studies covering the effect of pillar size and layer orientation with respect to the pillar axis in metal-ceramic nanolaminates are still scarce.
This work is mainly focused on the study, by micropillar compression, of the deformation and failure mechanisms of metal-ceramic Al/SiC nanolaminates, with layer thickness between 10 and 100 nm, as a function of layer orientation and pillar size,. Finite element modeling (FEM) was used to support the experimental observations, when needed. Deformation mechanisms and stress-strain behavior were determined for layers oriented at 0º, 45 º and 90º, for two different pillar sizes. The results revealed that the main initial deformation mechanism at room temperature was plasticity of the Al layers, constrained by the ceramic SiC layers, but that the final failure is very dependent on layer orientation and other microstructural features apart from layer thickness. While the micropillars loaded parallel (0º) and at 45º to the layers failed by the formation of shear and kink bands, triggered by the pre-existing layer waviness, micropillar loaded in the perpendicular direction fail by cracking of the SiC layers, without any appreciable effect of layer waviness. Two size effects were observed, one intrinsic and related to the individual thickness and the other, extrinsic, related to the pillar size. The origin and competition between these two size effects will be discussed.
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