Abstract
Composite materials usually possess a severe deformation incompatibility between the soft and hard phases. Here, we show how this incompatibility problem is overcome by a novel composite design. A gradient nanolayer-structured Cu-Zr material has been synthesized by magnetron sputtering and tested by micropillar compression. The interface spacing between the alternating Cu and Zr nanolayers increases gradually by one order of magnitude from 10 nm at the surface to 100 nm in the centre. The interface spacing gradient creates a mechanical gradient in the depth direction, which generates a deformation gradient during loading that accumulates a substantial amount of geometrically necessary dislocations. These dislocations render the component layers of originally high mechanical contrast compatible. As a result, we revealed a synergetic mechanical response in the material, which is characterized by fully compatible deformation between the constituent Cu and Zr nanolayers with different thicknesses, resulting in a maximum uniform layer strain of up to 60% in the composite. The deformed pillars have a smooth surface, validating the absence of deformation incompatibility between the layers. The joint deformation response is discussed in terms of a micromechanical finite element simulation.
Highlights
Composite materials play a central role in the development of novel engineering solutions, in the aerospace and automobile sectors[1,2]
The gradient nanolayer (GNL) Cu/Zr composites were synthesized by magnetron sputtering
GNL1 and GNL3, were prepared, in which multiple Zr-Cu bilayers with constituent thicknesses of 10 nm, 20 nm and 30 nm were included in one half of the sample, and the numerals ‘1’ or ‘3’ indicate the number of the above bilayers of each thickness
Summary
Composite materials play a central role in the development of novel engineering solutions, in the aerospace and automobile sectors[1,2]. The underlying artificial gradient structures that were utilized in these studies mainly included grain size gradients spanning over four orders of magnitude[53] or nanotwin gradients in twinning induced plasticity steel[54] These gradient approaches have proven to be a successful strategy for enhancing the mechanical properties through defect gradients without requiring alloy modifications[55], i.e., they were applied to pure metals or homogeneous solid solution alloys. We extend this idea to a multiphase composite material in order to take the first step towards solving the general problem of the deformation incompatibility encountered in nanolayered composites by utilizing structural gradients. We analysed the results and the boundary conditions using a micromechanical finite element (FE) simulation, which models the individual layers and their co-deformation in terms of an elastic-plastic constitutive description (Supplementary Note 1)
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