Study on fracture of tungsten wire induced by acoustic cavitation at different hydrostatic pressures and driving electric powers

摘要

The near-solid wall mull-bubble cavitation is an extremely complex phenomenon, and cavitation has strong erosiveness. The melting point (about 3410 degrees 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 aviation 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.