article · Modelling and Simulation in Materials Science and Engineering
Semi-coherent interfaces in metallic multilayers are traditionally viewed as barriers to dislocation motion that strengthen materials. Using molecular dynamics simulations, the mechanical response of semi-coherent body-centred cubic interfaces was investigated under different nano-indentation loading directions. By reversing the indentation direction in iron-vanadium bilayers, the interface unexpectedly shifts from acting as a barrier to serving as an active dislocation source and transmitter. This behaviour occurs because pre-existing misfit dislocations decompose into mobile dislocations within the vanadium substrate while the indented iron layer deforms elastically. Consequently, this interface-mediated plasticity triggers marked softening when the iron layer thickness falls below a critical threshold, contrasting with the strengthening observed in vanadium-iron bilayers. Identical mechanisms found in tantalum-tungsten bilayers confirm that this directional effect is a general characteristic of body-centred cubic semi-coherent interfaces, offering insights for interface engineering.
Understanding how nanoscale metallic boundaries respond to mechanical stress is crucial for designing durable layered components. Discovering that interfaces can cause softening rather than strengthening depending on the direction of loading challenges standard design assumptions. These findings provide foundational knowledge that helps materials researchers anticipate how nanoscale metallic multilayer systems deform under localised contact pressures.
This work is early-stage fundamental research conducted through atomistic simulations. The findings could inform materials scientists and interface engineering specialists aiming to optimise multilayered thin films and structural coatings against mechanical wear or failure. However, because the study is entirely computational and focuses on nanoscale deformation mechanisms, it remains at a low readiness level with no immediate commercial product or applied testing indicated in the abstract.
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Abstract Semi-coherent interfaces are widely recognized as effective barriers to dislocation motion and are therefore considered as a key strengthening element in metallic multilayers. However, whether this role remains unchanged under different nano-indentation loading directions is still largely unexplored. Using molecular dynamics simulations, this work demonstrates that the mechanical response of semi-coherent bcc interfaces is fundamentally governed by the indented layer. By simply reversing the indentation direction in Fe/V bilayers, the interface undergoes a remarkable transition from a dislocation barrier to an active dislocation source and transmitter. This transition is driven by the decomposition of the pre-existing <100> misfit dislocations into mobile 1/2<111> dislocations within the V substrate, while the indented Fe layer remains elastically deformed. As a result, interface-mediated plasticity induces pronounced softening when the Fe layer thickness falls below a critical value, in contrast to the strengthening observed for the V/Fe bilayer. The same deformation mechanisms are identified in Ta-W bilayers, demonstrating that the observed inverse interface effect is not material-specific but represents a general characteristic of bcc semi-coherent interfaces. These findings provide a new atomistic framework for understanding and tailoring the mechanical response of multilayered materials through interface engineering.
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DOI: 10.1088/1361-651x/ae9f7a
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