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中熵合金因其独特的强塑性协同效应，在高应变速率服役的结构材料领域展现出广阔应用前景。本研究聚焦于NiCoV中熵合金体系，通过引入高熔点钨元素（5 at.%）进行合金化设计，采用真空电弧熔炼结合热机械处理工艺制备了(NiCoV)95W5合金。基于分离式霍普金森压杆实验平台，系统揭示了该合金在2000-6000 s-1高应变速率下的动态响应机制与变形机理。研究发现：合金展现出优异的应变速率敏感性（m=0.42），当应变速率从准静态（10-3 s-1）提升至动态（6000 s-1）时，屈服强度显著提升162%（720→1887 MPa），这一强化效应源于高应变速率下晶格畸变诱导的声子拖曳作用显著增强。通过显微分析，揭示了该合金体系在高应变速率下的多尺度协同变形机理：2000 s-1时以位错平面滑移为主导，当速率增至4000 s-1时形成高密度位错缠结网络并激发部分析出相协同变形，而在6000 s-1条件下则通过诱发变形孪晶实现加工硬化的存续。本研究阐明了W元素掺杂的NiCoV中熵合金动态力学行为与变形机制，为设计具有优异动态力学响应的新型结构材料提供了参考。Medium-entropy alloys (MEAs), known for their outstanding strength and ductility, offer great potential for high strain-rate applications. This study focuses on a NiCoV-based MEA system, where a novel alloy design strategy was proposed by introducing 5 at.% high-melting-point tungsten through vacuum arc melting coupled with thermomechanical processing to fabricate the (NiCoV)95 W5 alloy. Split Hopkinson pressure bar (SHPB) experiments were conducted to elucidate the dynamic response mechanisms and deformation behavior under high strain rates (2000-6000 s-1). The results show that the enhanced phonon drag effect at elevated strain rates, caused by severe lattice distortion, leads to a substantial increase of 162% in yield strength from 720 MPa (10-3 s-1) to 1887 MPa (6000 s-1), accompanying with a relatively high strain-rate sensitivity (m = 0.42); Microscopic analysis revealed the multi-scale cooperative deformation mechanism of the alloy system under high strain rate. When the strain rate is 2000 s-1, the alloy exhibits a low dislocation density dominated by dislocation planar slip. As the strain rate rises to 4000 s-1, elevated flow stress and deformation promote substantial dislocation multiplication and entanglement into high-density dislocation cells. Dislocation pile-up stress induces co-deformation of precipitates and releases stress concentration at the phase interface. Upon further increasing the strain rate to 6000 s-1, severe plastic deformation induces nano-twin formation within the matrix, as prevailing strain hardening. This study illustrates the tungsten-doping mediated dynamic response mechanisms in MEAs, providing a guidance for designing novel structural materials with excellent dynamic mechanical responses.
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Keywords:
- Medium-entropy alloy /
- Dynamic compression deformation /
- Work hardening /
- Precipitation strengthening
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