Abstract The acoustic softening effect in metals during plastic deformation has been widely investigated in the past decades. However, the mechanism of such an acoustic plasticity remains controversial. As a result, several models were proposed to understand the acoustic softening effect in terms of stress superposition, thermal activation theory, crystal plastic theory and other mechanisms associated with dislocation evolution. In this study, we proposed a mechanism that the athermal dislocation dynamics may heterogeneously change at microstructure level during ultrasonic vibration assisted (UVA) deformation. Specifically, the work required to eject dislocations from grain boundaries may be altered by the acoustic energy absorption difference of a dislocation in the grain interior and one in the grain boundary. As a result, the acoustic softening effect on the Hall-Petch behavior was modeled by incorporating a power function of acoustic energy density into the dislocation ejection work. To validate the developed model, UVA micro-tension tests were conducted on pure titanium specimens. Results showed that the Hall-Petch slope decreased due to ultrasonic vibration, and the ultrasound-induced decrease of the Hall-Petch slope increased with plastic deformation. Note that our model predictions matched well with the experimental results at the lower strains, providing an alternative insight into the acoustic softening effect on the Hall-Petch behavior. Microstructure examinations showed that the superimposed ultrasonic vibration in micro-tension could lead to the retardation of texture evolution, the decreases in kernel average misorientation (KAM) value, low-angle grain boundary (LAGB) fraction and dislocation density in titanium foils, which somewhat supported our model assumptions in terms of the acoustic energy dependent reduction in dislocation density and the enhanced dislocation ejection causing the improvement of plastic compatibility.

中文翻译：

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超声振动辅助微张力中纯钛霍尔-佩奇行为的声学软化效应的基于能量的建模

摘要 在过去的几十年中，金属塑性变形过程中的声软化效应得到了广泛的研究。然而，这种声学可塑性的机制仍然存在争议。因此，提出了几种模型来理解应力叠加、热激活理论、晶体塑性理论和其他与位错演化相关的机制方面的声学软化效应。在这项研究中，我们提出了一种机制，即在超声振动辅助 (UVA) 变形过程中，非热位错动力学可能在微观结构水平上发生不均匀变化。具体而言，从晶界弹出位错所需的功可能会因晶内位错和晶界位错的声能吸收差异而改变。因此，通过将声能密度的幂函数结合到位错喷射功中来模拟对霍尔-佩奇行为的声软化效应。为了验证开发的模型，对纯钛样品进行了 UVA 微张力测试。结果表明，Hall-Petch 斜率因超声振动而减小，而Hall-Petch 斜率的超声诱导减小随着塑性变形而增大。请注意，我们的模型预测与较低应变下的实验结果非常吻合，提供了对霍尔-佩奇行为的声学软化效应的另一种见解。显微组织检测表明，微张力中叠加的超声振动会导致织构演化延迟，核平均取向差（KAM）值降低，