Abstract The plastic flow characteristics of body centered cubic metals, which is dominated by the motion of screw dislocations, generally exhibits strong strain rate dependence. In-situ scanning electron microscopy compression tests are performed on tungsten (W) single crystal nano and micro pillars, with diameters in the range 100-2000 nm. We demonstrate here that by reducing sample size, the strain rate sensitivity of plastic flow, including not only the yield strength but also the strain burst statistics, is reduced. It is found that the strain rate sensitivity of the flow stress scales with the sample size d as d 0 . 67 . Statistical analysis of the strain burst size displays truncated power law scaling with a lower exponent at higher strain rate for micron size pillars. Nano size pillars ( 500 nm) show near universal scaling exponent of 1 . 50 ± 0 . 07 at all applied strain rates. The strain hardening rate and deformation morphology are found not to be very sensitive to the strain rate. This external pillar sample size effect is further compared with the internal grain size in nanocrystalline W in order to guide the design of new materials by tuning the characteristic length scale (external or grain size)

中文翻译：

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纳米/微米样品尺寸对钨中塑性流动应变率敏感性的影响

摘要 体心立方金属的塑性流动特性受螺旋位错运动的支配，通常表现出很强的应变率依赖性。原位扫描电子显微镜压缩测试在钨 (W) 单晶纳米和微柱上进行，直径在 100-2000 nm 范围内。我们在这里证明，通过减少样本大小，塑性流动的应变率敏感性（不仅包括屈服强度，还包括应变爆发统计）降低。发现流动应力的应变率敏感性与样本大小 d 为 d 0 成比例。67 . 应变爆发尺寸的统计分析显示了截断的幂律缩放，​​在更高的应变速率下，微米尺寸的柱子具有较低的指数。纳米尺寸的柱子 (500 nm) 显示接近 1 的通用缩放指数。50±0。07 在所有应用应变率下。发现应变硬化速率和变形形态对应变速率不是很敏感。这种外部支柱样品尺寸效应与纳米晶 W 的内部晶粒尺寸进一步比较，以通过调整特征长度尺度（外部或晶粒尺寸）来指导新材料的设计