In Situ Study on the Nucleation, Growth Evolution, and Motion Behavior of Hydrogen Bubbles at the Liquid/Solid Bimetal Interface by Using Synchrotron Radiation X-Ray Imaging Technology

Pore defects at the liquid/solid interface contribute to the interfacial bonding quality. Understanding the formation and growth mechanism of pores can help control their size distribution and eliminate their formation. However, the traditional static-research methods limit the in-depth study of the dynamic evolution behavior of bubbles. The growth, motion behavior, and morphological evolution of hydrogen bubbles at the liquid/solid bimetal interface during heating were characterized in situ, using synchrotron radiation X-ray imaging technology, and the bubbles' nucleation, growth mechanisms, and motion characteristics were investigated. The results show that the nucleation mechanism of hydrogen bubbles contains heterogeneous nucleation and bifilms. Bubble growth is divided into two stages: the inhomogeneous composition and bifilm transformation into hydrogen bubbles. The relationship between the bubbles' mean diameter and heating time conform to the stochastic model. The growth mechanism of bubbles exhibits jump merging and annexation behaviors, accompanied by the morphological transformation from spherical to elliptic and irregular shapes. The motion of the hydrogen bubbles includes upward migration and astatic jumping. The bubbles' growth, hindered by intermetallic compounds (IMCs), has experienced several jumps, attributed to the transformation of bifilms into bubbles, increasing bubble size and deformation, IMC dissolution, and IMC disturbance.