Zhang Yurong, Zhang Zhenjun, Wu Junru, Liu Yalu, Zhang Mingjun, Yang Chenglin, He Min, Gong Xiaobo, Zhang Zhefeng, Wang Zhibiao, Li Faqi
State Key Laboratory of Ultrasound in Medicine and Engineering, College of Biomedical Engineering, Chongqing Medical University, Chongqing 400016, China.
Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China.
Ultrason Sonochem. 2020 Nov;68:105232. doi: 10.1016/j.ultsonch.2020.105232. Epub 2020 Jun 18.
The near-solid wall multi-bubble cavitation is an extremely complex phenomenon, and cavitation has strong erosiveness. The melting point (about 3410 °C) of tungsten is highest among all pure metals, and its hardness is also very high (its yield strength is greater than 1 GPa). What would happen to pure tungsten wire under extreme conditions caused by collapsing cavitation bubbles at high hydrostatic pressure? In this paper, we have studied the fracture process of pure tungsten wire with diameter of 0.2 mm mounted at the focus of a standing acoustic wave produced by a spherical cavity transducer with two open ends placed in a near spherical pressure container, and also studied the macro and micro morphological characteristics of the fracture and the surface damage at different fracture stages of tungsten wire under various hydrostatic pressures and driving electric powers. The results have shown that the fracture time of tungsten wire is inversely proportional to avitation intensity with hydrostatic pressure and driving electric power, the higher the acoustic pressure caused by higher electric power, the shorter the fracture time. The possible fracture mechanisms of tungsten wire in this situation we found mainly contributed to asymmetrically bubbles collapse near the surface of tungsten wire, leading to tearing the surface apart; consequently cracks along the radial and axial directions of a tungsten wire extend simultaneously, classified as trans-granular fracture and inter-granular fracture, respectively. With the increase of cavitation intensity, the cracks tend to extend more radially and the axial crack propagation path becomes shorter, that is, mainly for trans-granular fracture; with the decrease of cavitation intensity, intergranular fracture becomes more obvious. When the hydrostatic pressure was 10 MPa and the driving electric power was 2 kW, the fibers became softener due to the fracture of the tungsten wire. The fracture caused by acoustic cavitation was different from conventional mechanical fracture, such as tensile, shear, fatigue fracture, on macro and micro morphology.
近固壁多泡空化是一种极其复杂的现象，且空化具有很强的侵蚀性。钨的熔点（约3410℃）在所有纯金属中是最高的，其硬度也非常高（其屈服强度大于1GPa）。在高静水压力下空化泡溃灭所造成的极端条件下，纯钨丝会发生什么情况呢？在本文中，我们研究了直径为0.2mm的纯钨丝的断裂过程，该钨丝安装在一个两端开口的球形腔换能器产生的驻波焦点处，该换能器置于一个近似球形的压力容器中，同时还研究了在不同静水压力和驱动电功率下钨丝在不同断裂阶段的宏观和微观断裂形态特征以及表面损伤情况。结果表明，钨丝的断裂时间与空化强度、静水压力和驱动电功率成反比，电功率越高导致的声压越高，断裂时间越短。我们发现，在这种情况下钨丝可能的断裂机制主要是由于钨丝表面附近的气泡不对称溃灭，导致表面撕裂；随后，沿钨丝径向和轴向的裂纹同时扩展，分别归类为穿晶断裂和沿晶断裂。随着空化强度的增加，裂纹倾向于更多地沿径向扩展，轴向裂纹扩展路径变短，即主要为穿晶断裂；随着空化强度的降低，沿晶断裂变得更加明显。当静水压力为10MPa且驱动电功率为2kW时，由于钨丝断裂，纤维变得更柔软。声空化引起的断裂在宏观和微观形态上与传统的机械断裂（如拉伸、剪切、疲劳断裂）不同
