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首页> 外文期刊>Materials Science and Engineering >Microstructural evolution of adiabatic shear bands in pure copper during impact at high strain rates
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Microstructural evolution of adiabatic shear bands in pure copper during impact at high strain rates

机译：高应变速率冲击过程中纯铜中绝热剪切带的组织演变

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A systematic study was conducted on copper of commercial purity (99.9% purity) to elucidate the sequence of events that leads to the evolution of adiabatic shear bands and the structure of the evolved shear bands after strain localization during deformation at high strain rates and large strains. A direct impact Hopkinson Pressure Bar was used to deform different specimens at increasing impact momentum and strain rate followed by microstructural characterization using metallographic techniques and transmission electron microscopy. It was observed that sequential occurrence of emergence of dislocations from grain and twin boundaries, formation of dislocation cell structures and substructures with varying cell sizes and cell walls, dislocation-nucleation controlled softening and extensive micro twinning characterized the structure of the evolved adiabatic shear bands as a function of impact momentum and strain rate. The dislocation cell structures and substructures were typically made up of high-density dislocation walls surrounding low-density dislocation cell interiors. The mi-crohardness distribution within the evolved shear bands increased up to a peak value at a critical impact momentum and strain rate (≥ 45kg m/s and ≥ 6827 s~(-1)). Above this threshold, microhardness of the regions within the evolved shear bands decreased because of the occurrence of softening. However, the first specimen that exhibited softening had high-density dislocation cell walls surrounding dislocation-free cell interiors with no observed recrystallized grains. Despite the onset of softening both within and outside the shear bands, the regions within the shear bands were always harder than the regions outside the shear bands. The shear bands that exhibited significant softening were clad with vast distribution of microtwins in addition to evolved refined grains and sub-grains. It is discussed that thermally activated dislocation processes as a result of the rise in temperature during impact, dynamic recovery and dynamic recrystallization do not necessarily result in strain localization in the impacted copper specimens because their effects are observed in the structure of the evolved shear bands at a latter stage when strain localization had already occurred.
机译：对商业纯度（纯度为99.9％）的铜进行了系统的研究，以阐明导致绝热剪切带演变的事件顺序以及在高应变率和大应变下的变形过程中应变局部化后所形成的剪切带的结构。 。使用直接冲击霍普金森压力棒使冲击动量和应变率增加时使不同的样品变形，然后使用金相技术和透射电子显微镜对显微组织进行表征。据观察，从晶界和孪晶界开始出现位错，形成具有不同晶胞尺寸和胞壁的位错细胞结构和亚结构，位错成核控制的软化和广泛的微孪晶的顺序发生，都表明了绝热剪切带的结构如下：冲击动量和应变率的函数。位错单元的结构和子结构通常由围绕低密度位错单元内部的高密度位错壁组成。在临界冲击动量和应变速率（≥45kg m / s和≥6827 s〜（-1））下，演化剪切带内的显微硬度分布增加到峰值。高于该阈值，由于发生软化，在所形成的剪切带内的区域的显微硬度降低。但是，第一个表现出软化的样品具有高密度的位错细胞壁，周围是无位错的细胞内部，没有观察到重结晶晶粒。尽管剪切带内部和外部都开始软化，但是剪切带内的区域总是比剪切带外的区域硬。表现出明显软化的剪切带除了细化晶粒和亚晶粒外，还分布着大量的微晶。讨论了由于在冲击，动态恢复和动态再结晶过程中温度升高而导致的热活化位错过程不一定会在受冲击的铜试样中导致应变局部化，因为它们的影响在扩展的剪切带结构中观察到。应变本地化已经发生的后期。

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