This study aims to explore the mode of Zn transportation and the failure mechanism of cracking associated with liquid metal embrittlement (LME) using fractography as the key technique. A three-point bend test was performed on a TRIP steel resistance spot weld to open the LME crack in the form of a free fracture surface for the fractographic investigation. The presence of liquid Zn on the fracture surface was revealed by the Fe-Zn phase transformation and the spike-like morphology of the residual Zn, confirming that the mode of Zn transportation in LME cracks was liquid penetration through the austenite grain boundary. In addition, the fractography of the bend test samples and electron backscattered diffraction of the cracks revealed the failure mode of the LME crack as a complete intergranular brittle fracture without the generation of any microplasticity. Thus, the underlying failure mechanism of cracking in Zn-LME can be explained by the Stoloff-Johnson-Westwood-Kamdar brittle fracture model induced by the decohesion of interatomic bonds. Overall, a dramatic reduction in the interatomic bond strength by lowering the surface energy of the grain boundary with liquid Zn penetration causes the decohesion-induced intergranular brittle cracking.

本研究旨在通过分形照相技术探索锌的运输方式以及与液态金属脆化有关的裂纹破坏机理。在TRIP钢的电阻点焊上进行了三点弯曲测试，以自由断裂表面的形式打开LME裂纹，以进行分形研究。Fe-Zn相变和残余Zn的峰状形态揭示了在断裂表面上存在液态Zn，证实了LME裂纹中Zn的传输方式是液体通过奥氏体晶界渗透。此外，弯曲测试样品的分形图和裂纹的电子反向散射衍射显示，LME裂纹的破坏模式是一个完整的晶间脆性断裂，没有任何微塑性的产生。因此，Zn-LME开裂的潜在破坏机理可以通过由原子间键解聚引起的Stoloff-Johnson-Westwood-Kamdar脆性断裂模型来解释。总体而言，随着液态锌的渗透，通过降低晶界的表面能，原子间键合强度的显着降低会引起脱粘作用引起的晶间脆性开裂。