Micro-crystallographically revealing the plasticity-evolved behaviors of thick Ti–6Al–4V laser-arc hybrid welded joint

Abstract

Revealing the plasticity-evolved behaviors is of great significance for developing high-reliability thick Ti–6Al–4V welded joint for deep-sea exploration equipment. This research effort entailed a collaborative utilization of transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques to reveal the evolution behaviors of microstructure, weld texture, and grain boundaries for thick Ti–6Al–4V laser-arc hybrid welded joint with thickness of up to 40 mm. The discerned outcomes of this study underscored that the mixture strategy of large-sized lath martensite, densely entangled dislocations, and dislocations pile up at grain boundaries in distinct welding layers significantly enlarged the inhomogeneous plasticity of thick Ti–6Al–4V welded joint. Besides, the intensified cylindrical-texture within the weld leads to a substantial augmentation in the occurrence of Schmidt Factor concentrations above 0.3, indicative of a larger fraction of grains assuming a soft-orientation. Furthermore, the investigation unveiled an increase in the proportion of low angle grain boundaries demonstrably augmented the distribution density of geometrically necessary dislocations (GNDs) within the welds, which in conjunction with the enhanced cylindrical texture substantially elevated the grains deformability, consequently reinforcing the plasticity of welded joint. This work has provided insights into the evolution behavior of thick Ti–6Al–4V welded joint for greatly improving the plastic properties of welded structure, and substantially enhancing the service safety for deep-sea exploration equipment.