Intergranular/transgranular fracture in the liquid metal embrittlement of polycrystalline zinc

Tensile tests were performed on polycrystalline Zn specimens in contact with liquid Ga, In, In–Bi eutectic alloy, or Sn–Bi eutectic alloy below 450 K. These low-melting-point metals and alloys embrittled Zn specimens when they were in the liquid state. Although single-crystalline Zn is known to be embrittled by liquid Ga, intergranular cracking occurred in polycrystalline Zn in the presence of liquid Ga, while transgranular cracking occurred in the presence of In and Sn. Just above the melting point of Ga, only Ga atoms were found to penetrate along the grain boundaries of polycrystalline Zn. Although all these embrittlers reduced the cleavage fracture stress, only Ga atoms in the grain boundaries significantly reduced the strength of the grain boundaries, resulting in intergranular cracking. For the specimens in contact with liquid Ga, the incidence of transgranular cleavage fractures increased at high temperatures due to the reduction in the number of Ga atoms in the grain boundaries by diffusion into the grains.