The Evolution of Strain Gradient and Anisotropy in Gradient-Structured Metal

et al. 2021

Sci. China Mater.

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Gradient structure (GS) possesses a typical trans-scale grain hierarchy with varying internal plastic stability, and the mutual plastic accommodation plays a crucial role in its superior strength-ductility combination. Using the in-situ synchrotron X-ray diffraction (XRD) during tensile loading, we measured lattice strains sequentially from the nanostructured (NS) surface layer to the central coarsegrained (CG) layer to elucidate when and how plastic accommodation occurs and evolves within the GS, along with their roles in plastic deformation and strain hardening. Throughout the tensile deformation, two types of plastic incompatibility occur in the GS. One is an extended elastoplastic transition due to layer-by-layer yielding. The other is strain localization and softening in the NS layer, in contrast with the stable plastic deformation in the CG layer. Plastic accommodation thus occurs concurrently and manifests as both an inter-layer and intra-layer change of stress state throughout tensile deformation. This produces different micromechanical responses between layers. Specifically, the NS layer initially experiences strain hardening followed by an elastoplastic deformation. The hetero-deformation induced hardening, along with forest hardening, facilitates a sustainable tensile strain in the NS layer, comparable to that in the CG layer.

Section: Layer-by-layer Yieldingmentioning

confidence: 99%

Plastic accommodation during tensile deformation of gradient structure

et al. 2021

Sci. China Mater.

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“…The facet size for the strain calculation using DIC method was 50 μm. The other details for the DIC method can be found in our recent paper 48 .…”

Section: Materials and Experimental Proceduresmentioning

confidence: 99%

Plastic deformation mechanisms in a severely deformed Fe-Ni-Al-C alloy with superior tensile properties

Jiang

et al. 2017

Sci Rep

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Nanostructured metals have high strength while they usually exhibit limited uniform elongation. While, a yield strength of approximately 2.1 GPa and a uniform elongation of about 26% were achieved in a severely deformed Fe-24.8%Ni-6.0%Al-0.38%C alloy in the present work. The plastic deformation mechanisms for the coarse-grained (CG) sample and the cold-rolled (CR) samples of this alloy were investigated by a series of mechanical tests and microstructure characterizations before and after tensile tests. No obvious phase transformation was observed during the tensile deformation for the CG sample, and the plastic deformation was found to be mainly accommodated by deformation twins and dislocation behaviors. While significant phase transformation occurs for the CR samples due to the facts that the deformed grains by CR are insufficient to sustain the tensile deformation themselves and the flow stress for the CR samples is high enough to activate the martensite transformation. The amount of phase transformation increases with increasing thickness reduction of CR, resulting in excellent tensile ductility in the severely deformed alloy. The back stress hardening was found to play a more important role in the CR samples than in the CG sample due to the dynamically reinforced heterogeneous microstructure by phase transformation.

“…Moreover, we reported an "in-situ" evolution of the induced strain gradients in a gradient-structured metals during uniaxial tension [57]. We found that the lateral strain gradients increase with increasing applied tensile strain, and the strain gradients increase faster and the back-stress hardening plays more important role at the elasto-plastic transition stage.…”

Section: Tensile Behaviors Of Gradient Grained Structuresmentioning

confidence: 90%

A Review on Heterogeneous Nanostructures: A Strategy for Superior Mechanical Properties in Metals

Yuan

et al. 2019

Metals

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Generally, strength and ductility are mutually exclusive in homogeneous metals. Nanostructured metals can have much higher strength when compared to their coarse-grained counterparts, while simple microstructure refinement to nanoscale generally results in poor strain hardening and limited ductility. In recent years, heterogeneous nanostructures in metals have been proven to be a new strategy to achieve unprecedented mechanical properties that are not accessible to their homogeneous counterparts. Here, we review recent advances in overcoming this strength–ductility trade-off by the designs of several heterogeneous nanostructures in metals: heterogeneous grain/lamellar/phase structures, gradient structure, nanotwinned structure and structure with nanoprecipitates. These structural heterogeneities can induce stress/strain partitioning between domains with dramatically different strengths, strain gradients and geometrically necessary dislocations near domain interfaces, and back-stress strengthening/hardening for high strength and large ductility. This review also provides the guideline for optimizing the mechanical properties in heterogeneous nanostructures by highlighting future challenges and opportunities.