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中国物理学会期刊

脉冲电流对典型枢轨材料高应变率剪切行为的作用规律

CSTR: 32037.14.aps.75.20251475

Influence of pulsed current on high strain rate shear behavior of typical armature and rail materials

CSTR: 32037.14.aps.75.20251475
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  • 绝热剪切带(ASB)是高应变率剪切冲击下诱导损伤的重要机制, 而大电流密度下枢轨材料高速剪切变形机理尚不明晰. 本文开展了高应变率(≥104 s–1)耦合大电流密度(≥108 A/m2)下典型枢轨材料剪切变形特性研究. 结果表明, ASB形成能垒从高到低为: 紫铜、无氧铜、CuCrZr合金、Al2O3弥散强化铜合金、黄铜和7075铝合金, 因此7075铝最易形成ASB, 黄铜次之, 其他铜基轨道难以观测到ASB. 7075铝和黄铜中均表现出电流对裂纹及ASB形成的抑制作用. 电子背散射衍射结果显示, 7075铝剪切带内存在大量细小等轴晶粒, 晶粒择优取向较基体明显转变, 随电流密度升高, 带内晶粒尺寸增大, 动态再结晶比例显著下降. 机械辅助旋转动态再结晶可合理解释超细晶形成与织构演化. 研究指出热软化不足以诱导ASB形成, 旋转动态再结晶软化是其主要成因. 根据实测高应变率载流下的屈服强度, 计算得到载流下7075铝ASB宽度, 发现脉冲电流引起的温升与屈服强度降低导致ASB宽化, 使得能量耗散增强, 抑制了动态再结晶, 从而阻碍了ASB的产生.

     

    Adiabatic shear bands (ASBs) are a critical mechanism for inducing damage under high strain-rate shear impact, whereas the mechanism of high-current-density-induced shear deformation of armature and rail materials remains unclear. This study employs a pulsed power source and an electromagnetic repulsion disk device to investigate the shear deformation characteristics of typical armature and rail materials under high strain rates (≥104 s–1) coupled with high current densities (≥108 A/m2). The results show that the ASB formation energy barrier decreases in the following order: pure copper, oxygen-free copper, CuCrZr alloy, Al2O3 dispersion-strengthened copper alloy, brass, and 7075 aluminum alloy. Therefore, 7075 aluminum alloy is the most prone to ASB formation, followed by brass, whereas other copper-based rail materials rarely exhibit ASB features. Both 7075 aluminum alloy and brass exhibit a current-induced suppression effect on crack propagation and ASB formation. Electron backscatter diffraction (EBSD) analysis reveals that numerous fine equiaxed grains are present within the shear bands of 7075 aluminum, and the texture within the bands significantly differs from that of the surrounding matrix. As current density increases, the grain size within the band increases, while the fraction of dynamically recrystallized grains decreases markedly. The formation of ultrafine grains and the texture evolution can be reasonably explained by mechanically assisted rotational dynamic recrystallization. The results indicate that thermal softening alone is insufficient to induce ASB formation; instead, softening caused by rotational dynamic recrystallization is the dominant mechanism. The current-induced temperature rise is calculated, and the yield strength decrease under high-strain-rate current loading is measured, based on which the width of adiabatic shear bands (ASBs) under current is determined. The theoretical predictions show that they are in good agreement with experimental results. The results indicate that the temperature rise and softening effect induced by pulsed current lead to an increase in ASB width, which intensifies energy dissipation, suppresses dynamic recrystallization, and inhibits the formation of adiabatic shear bands.

     

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